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HISTORY OF CHEMISTRY 



BY 

FRANCIS P. VENABLE, Ph.D., D.Sc, LL.D. 



D. C. HEATH & CO., PUBLISHERS 

BOSTON NEW YORK CHICAGO 






Copyright, 1922, 
By D. C. Heath & Co. 

2p2 



PRINTED IN U.S.A. 

JUL 10 1922 

©CLAG774 81 



PREFACE 

The first edition of this book appeared in 1894. While 
it has passed through a number of editions since, there has 
been no attempt to bring it up to date nor to revise it in 
any way, and ahhough there has been much to preoccupy 
me, especially in other lines of work, I recognize the fact 
that there has been no excuse for such neglect. 

It has now been entirely rewritten on a changed plan 
of arrangement and made to cover the great progress in 
the science which has taken place since it first appeared. 
Some material considered unnecessary has been eUminated 
so that it might be kept within the same compass that has 
proved so convenient for those who could not devote to 
the subject the time required by the larger treatises. 

Francis P. Venable 
Chapel Hill, N. G. 
June, 1922 



111 



CONTENTS 

PAGE 

Chapter I. THE BEGINNINGS 1 

Evolution of Science. — Industrial Arts, Metallurgy. — 
Minerals and Salts. — Glass Making and Pottery. — 
Dyeing and Tanning. — Soaps and Medicaments. 

Chapter II. EARLY DEVELOPMENT 8 

Naming the Science. — Arrangement of Facts. — Mysti- 
cism. — Manuscripts and Original Sources. — Laws. — 
Mutability in Nature. — Theories. — Atomic Theory. — 
Atoms. — Ether. — Indivisibility of the Atom. — World 
Building. — Apparatus. 

Chapter III. THE DARK AGES 19 

The Old Order Overturned. — Progress made by the 
Arabians. — Transmutation of Metals. — Geber. — 
New Substances. 

Chapter IV. THE MIDDLE AGES 24 

Albertus Magnus. — Roger Bacon. — Changes in the 
Sixteenth Century. — Paracelsus. — Agricola. — Van 
Helmont. — Glauber. — Rise of Theory. — Robert 
Boyle. — Experiments upon Air. — Constitution of 
Matter. 

Chapter V. THE CHEMISTRY OF COMBUSTION . 34 
Phlogiston Theory. — Composition of Air. — Hooke's 
Theory of Combustion. 

Chapter VI. THE NEW CHEMISTRY 38 

Analysis. — Scheele. — Analysis of Air. — Boerhaave. — 
Fixity of Proportions. — Berthollet. — Views as to 
Affinity. — Lavoisier. — Character of his Work. — 
Experiments on Combustion. — Composition of the 
Atmosphere. 



vi CONTENTS . j 

PAGE - 

Chapter VII. THE FOUNDATIONS 48 ' 

Composition of Water. — Transmutation of Water. — ! 

The Atmosphere. — Nature of Heat and Matter. — I 

Theory as to Acids. — Elements. — Spread of the New ■ 

Chemistry. — Black. — Priestley. — Discovery of Oxy- ] 

gen. — Study of the Atmosphere. — Views as to Com- ! 

bustion. I 

Chapter VIII. THE ATOMIC THEORY 59 ; 

Propositions of Lavoisier. — Richter. — Dalton^s Atomic 

Theory. — Constitution of Mixed Gases. — Law of \ 

Constant Proportions. — Law of Multiple Proportions. 

— Weights of the Atoms. — Dalton's Rules. — Gay- 

Lussac. — Law of Volumes. — Avogadro's Theory. ' 

Chapter IX. THE ATOMIC WEIGHTS 70 \ 

The Standard for the Atomic Weights. — WoUaston's i 
Equivalents. — Law of Specific Heats. — Isomorphism. 

— Electro-Chemical Equivalents. — Work of Dumas. — i 
Vapor Densities. — Gmelin's Views. — Confusion in the I 
Sixth Decade. — Revisions of the Atomic Weights. — I 
Clearing up the confusion. — Constancy of the Atomic j 
Weights. j 

J 
Chapter X. NATURE OF THE ELEMENTARY ATOM 81 
Prout's Hypothesis. — Views of Berzelius. — Testing 
the Hypothesis. — Numerical Relations. — Ascending 
Series. — Periodic System. — Zero Group. — Contri- 
butions from Radioactivity. — Composite nature of the > 
Atom. — Evidence as^to complexity. j 

Chapter XL AFFINITY, THE ATOMIC ATTRAC- | 

TIVE FORCE 90 ! 

Strength of Affinity. — Measurement of Affinity. — 
Valence. — Evolution of the idea. — Organo-Metallic 

Compounds. — Polybasic Acids. — Polyatomicity. — i 

Deduction from Inorganic Compounds. — Progress | 

made. j 

Chapter XII. GROWTH OF INORGANIC ' 

CHEMISTRY 99 j 

Discovery of New Elements. — Humphrey Davy. — I 

Decomposition of the Alkalis. — Composition of Muria- j 



CONTENTS vii 

PAGE 

tic Acid. — New Theory of Acids. — Alkalizing Prin- 
ciple. — Berzelius. — Contributions of Berzelius. — 
Analytical and Experimental Work. — Determination of 
Atomic Weights. — Introduction of Symbols. — DuaHs- 
tic Theory. — Additions to hst of Elements. — Mona- 
tomic Gases. — Further Development of Inorganic 
Chemistry. 

Chapter XIII. THE DEVELOPMENT OF ORGANIC 

CHEMISTRY 115 

Views of Lavoisier. — Views of Berzelius. — Isomerism. 

— Synthesis of Urea. — Organic Analysis, — Classifi- 
cation of Organic Substances. — Extension of the Elec- 
tro-Chemical Theory. — Extension of Radical Theory. 

— Benzoic Acid Radical. — Changes in Radical Theory. 

— Compound Radicals. 

Chapter XIV. FURTHER THEORIES AS TO 

STRUCTURE 126 

Atomic Theory confirmed. — Substitution Theory and 
Overthrow of Duahsm. — Substitution of Chlorine for 
Hydrogen. — Trichloracetic Acid. — Unitary Theory. 

— Nucleus Theory. — Type Theory. — Homologous 
Series. — Application of Valence Theory. — Benzene 
Theory. — Stereochemistry. — Pasteur. — Syntheses 
from Coal Tar. 

Chapter XV. PHYSICAL CHEMISTRY 138 

Law of Mass Action. — Electrolytic Dissociation. — 
Physical Properties of Solutions. — Osmotic Pressure. 

— Experiments of Van't Hoff. — Ionization Theory. — 
Colloidal Chemistry. 

Chapter XVL BIOCHEMISTRY .146 

Account of its Development. 

Chapter XVII. RADIOACTIVITY 150 

The Discovery. — Radium. — The Radiations. — 
Radioactive Substances. — Disintegration Theory. — 
Constitution of the Atom. — The New Atom and its 
Properties. — Factors in Element Formation. — Iso- 
topes. — Matter and the Universe. 



HISTOKY OF CHEMISTEY 

CHAPTER I 

THE BEGINNINGS 

Evolution of Science. — In attempting to discover 
traces of a science in earliest historic times one must 
first free his mind of the idea that he will find it in any- 
thing hke the elaborated modern form in which he knows 
it. These natural sciences are the result of a long and 
laborious process of evolution. First comes the gather- 
ing of facts and observations, and so the beginnings go 
far back of history to the earHest representatives of the 
race. The early motive was the struggle to maintain 
Hfe and increase bodily comforts, and this motive has 
not lost its force in the modern world. Man is a weapon- 
using and tool-making animal and so gathered and fash- 
ioned the objects which best served his purposes. Com- 
fort demanded clothing and shelter; therefore, he be- 
came weaver, tanner, and builder of houses. His higher 
nature developed the love of beauty and so he sought 
out paints and dyes; his ailments forced upon him some 
knowledge of remedies and medicines. With the change 
from nomad to citizen his necessities became greater 
and his inventive genius was stimulated. Trades and 
industries arose and with these came specialization in 
labor and formulation of knowledge. 

Yet there was nothing which could be called science 
and all is still beyond recorded history. The beginnings 

1 



2 HISTORY OF CHEMISTRY 

described were found wherever civilization centered — 
in Mesopotamia, China, India, Egypt, and European 
Greece. The growth of knowledge through experience, 
or empiricism, is exceedingly slow. Yet a number of in- 
dustrial arts sprang up and some were carried on with a 
high degree of skill. Artificial aids and labor-saving 
machinery, such as the blast furnace and potter's wheel, 
were called into use. There were invented tools making 
use of physical laws, even though these laws were not 
recognized or understood. Among these were the 
wedge, the lever, the screw, the wheel. Improvement 
and wider application of these fundamentals came with 
growing understanding of principles involved. 

Industrial Arts : Metallurgy. — An outline of the 
knowledge attained in some of these arts, many of which 
date back to the most remote antiquity, may well be con- 
sidered here. Taking up metallurgy first we find that 
six metals were well known — gold, silver, tin, iron, 
copper, and lead. Homer mentions these six and the 
Bi|ble does also; so they seem to have been in use from 
very ancient times. Mercury was afterwards added 
to the list. The derivation of the word metal is from 
the Greek word AteraXXaco, to search after, and the noun 
first meant or referred to mines. The ancients, espe- 
cially the Egyptians, were very skillful workers in metals. 
They made gold wire and leaf and fine inlaid work. 
Gold was apparently the first known of the metals. 
Its color, lustre, and malleability, as well as its freedom 
from tarnish and corrosion, attracted the attention of 
the early peoples. Its rarity and value soon brought 
it into use as a medium of exchange, and very early coins 
have been preserved. Its occurrence in the free state 



THE BEGINNINGS 3 

would doubtless account for its being recognized and 
used among the first of the metals. Early vessels were 
made from it, as witness those which have been found 
in ancient Troy. It was also used for coating or plating 
wood and other materials. 

Silver seems to have become known and to have been 
used at about the same time as gold. It also was found 
free and was easily made ready for use. Then follow 
copper, iron, tin, and lead. The Egyptians attributed 
the discovery of the metals to their sovereigns; the 
Phoenicians and other peoples to their divinities. 

The purification of gold and silver by the cupella- 
tion process was known before the Christian era, but 
there was no means known for the separation of gold 
from silver. The alloy of the two metals, in which enough 
silver was present to whiten the whole, was often found 
and was called eledrunij being regarded as a distinct 
metal from the others. Letters made of electrum a foot 
or more in height, which had been fastened to the walls 
of the temples, were found in the ruins of Herculaneum. 
The oldest coins were made of white or pale gold. After 
a while it was found that this alloy could be made arti- 
ficially by melting together three parts of gold and one 
of silver. 

Copper was in use before iron and was called x^X/cos 
by Homer. From this we get the names for certain 
copper minerals, as chalcopyrite and others. The Romans 
obtained it first from the island of Cyprus and called it 
aes cypriuMj and from this it became cuprum, a name 
used now in connection with its salts. It was used mainly 
in alloys, as with gold for coinage and jewelry and with 
zinc as brass. Zinc itself was unknown to them but the 



4 HISTORY OF CHEMISTRY 

ore was used along with the copper in making brass. 
Bronze was an alloy of copper and tin and was known 
also before the method of extracting tin from its ore had 
been discovered. This was very strong, much easier to 
prepare than iron, and more readily worked into shape. 
It was therefore a more abundant and cheaper material 
and was used for many purposes where we use iron. 
Weapons and many utensils were made from it. There is 
a tradition that the Egyptians knew a way of hardening 
and tempering copper without allojdng it and that this 
is one of the so-called lost arts. 

Iron was known in very early times. As it rusts so 
easily, very few early implements have come down to 
us. It had to be extracted from its ore. Probably through 
some happy accident the method became known. For 
many centuries down into modern times the art has 
been practised in India. A little pure ore mixed with 
charcoal was heated by a blow-pipe and a small lump 
of iron was produced. These lumps were heated and 
hammered together and a serviceable cutlery steel ob- 
tained. The early Egyptians understood how to harden 
or temper iron and quite possibly used such iron imple- 
ments in part of the work of constructing the pjo-amids. 
Iron was coined by the Greeks and in the time of Homer 
they used it for axes and ploughshares. The difficulty 
of reducing iron from its ores on a large scale would 
account for its not being used more largely and at an 
earlier time. 

Tin was obtained from India and Spain and after- 
wards from Britain. It was one of the articles of com- 
merce used in trade by the Phoenicians. Mirrors were 
made of it and copper vessels were coated over with it. 



THE BEGINNINGS 5 

Lead and tin seem to have been regarded as varieties 
of the same metal and were called plumbum nigrum 
and plumbum candidum respectively. Pliny writes of 
conveying water in lead pipes and Homer makes much 
earUer mention of the metal. It came mainly from 
Spain and Britain. From the former country mercury 
also was obtained and was used, as now, in extracting 
gold from its ores. Native mercury was called argentum 
vivum or quicksilver. 

Minerals and Salts. — The two oxides of copper, as 
they occur in nature, were used in glass making; ver- 
digris was manufactured and put to several uses; white 
lead was used as a cosmetic by the Athenian ladies and 
found further use as a medicine; red lead was used as 
a paint. The native antimony sulphide was used to 
paint the eyebrows and is still used for that purpose 
in the East under the name kohl. Black oxide of man- 
ganese was used in glass making for clearing up colored 
or darkened glass and so received the name pyrolusite. 
The native carbonate of zinc was used in making brass; 
the two sulphides of arsenic were well-known pigments. 
According to Davy, the ancient Greeks and Romans 
used almost the same colors as those employed by Ital- 
ian artists at the period of the revival of art in Italy. 

Soda and potash were used in washing and whitening 
clothes and in saponifying fats for soaps and unguents. 
Lime was burned and mortar made from it, though the 
earliest cementing materials seem to have been pitch and 
bitumen. Excellent hydraulic cement was made and used 
by the Romans in their great aqueducts. Salt and salt- 
peter were used as food preservatives. Alum was used 
in dyeing. Vinegar was the only acid known. 



6 HISTORY OF CHEMISTRY 

Glass Making and Pottery. — The art of glass making 
is very old and seems to have originated with the Egyp- 
tians. An account of its accidental discovery by the 
Phoenicians has also been handed down. Certainly the 
Egyptians reached a high proficiency in making glass, 
coloring and forming it, and also in the production of 
imitation precious stones. They were unable, however, 
to produce clear, colorless, and flawless glass. The seat 
of the industry was later transferred to Byzantium, 
the capital of the Eastern Empire, and the art of glass 
making was brought to Europe by the early crusaders, 
as also a number of other industries were brought back. 

The making of bricks and pottery must have been 
one of the earliest efforts of man in the line of manufac- 
ture. The potter and the potter's wheel were known 
among all the ancient peoples. Specimens of pottery 
have been unearthed from the earhest ruins. With the 
introduction of enamels, glazes, and decorations it be- 
came an art, and in this both the Etruscans and Egyp- 
tians excelled. The Chinese alone of the early nations 
knew how to make porcelain. 

Dyeing and Tanning. — Dyeing was carried to great 
perfection. Many plant and animal coloring matters 
were known. Mordants were used and the effects pro- 
duced were very beautiful. Paints were also prepared 
and appUed with brushes. The following mineral colors 
were known at the time of Pliny: White lead, red lead, 
zinc white, cinnabar, smalt, verdigris, ochre, lampblack, 
realgar, orpiment, stibnite, and the oxides of copper. 

Leather was first tanned by means of oils and later 
with bark, very much after the methods now in use. 
The hair was removed by means of lime. Some leather, 



THE BEGINNINGS 7 

tanned centuries before the Christian era, has been found 
in modern times in a state of fair preservation. 

Soaps and Medicaments. — Soap was made by mix- 
ing wood ashes with animal fats, thus saponifying them. 
It was used chiefly as a kind of pomatum; unguents, 
oils, etc., were rubbed upon the body in the place of 
soap as used in modern times. Both hard and soft soap 
were known. Burnt Ume was often added in its manu- 
facture. 

Many substances were used as medicaments. Some 
of these might be called chemical preparations, showing 
an early union between chemistry and pharmacy. Lead 
plasters were made from litharge and oil; iron rust was 
used and also alum, soda, and bluestone. Sulphur was 
employed as a disinfectant and also for bleaching pur- 
poses. Mineral waters were used and likewise various 
infusions from plants. 

Of course all races, and even the lower animals, had 
in the lapse of time discovered in plants and minerals 
sundry remedies for their ailing bodies. In the case of 
man the cures were often brought about then as now by 
psychic suggestion rather than through the actual cura- 
tive properties of the substances themselves. Disease 
was caused by the presence of an evil spirit which had 
to be exorcised before health could be restored. Thus 
Homer refers to the use of sulphur to drive away the 
evil spirits. The first chemists, then, who stored up 
knowledge of chemical substances might be classed as 
healers, and the earliest documentary evidences were in 
the form of lists of remedies and cures. Such papyri 
have been found in early Egyptian tombs. 



CHAPTER II 

EARLY DEVELOPMENT 

Naming the Science. — As has been shown, chemistry- 
early became allied with so-called magic and witch- 
craft, and those who practised it were usually feared 
and held in bad repute. It is probably this association 
which gave the name to the science. The Greek word 
xr/M^ia is manifestly a rendering of the Egyptian name 
chema or chemi. Plutarch tells us that chemia was a 
name given Egypt on account of its black soil, and that 
this term further meant the black of the eye, symbol- 
izing that which was obscure or hidden. The Coptic 
word khems or chems is closely related to this and also 
signifies obscure, occult; and with this is connected the 
Arabic chema, to hide. It was, therefore, the occult 
or hidden science, the black art. 

Arrangement of Facts. — The second stage in the 
evolution of the science is the gathering together of 
facts and observations and their systematic arranging 
and recording. A beginning of this had been made in 
so far as they were related to medicine but even there 
few traces are left. The conception of knowledge having 
any value apart from its immediate use in the service 
of man was slow to arise. Further, those who sought 
such knowledge were largely charlatans and quacks 
who had nothing to gain by enlightening their dupes 
and feared prosecution and punishment. 

8 



EARLY DEVELOPMENT 9 

Mysticism. — The earliest writings were lost or de- 
stroyed. For instance, Diocletian is said to have burned 
all of the Egyptian manuscripts bearing on alchemy 
because, as he said, these taught the art of making gold 
and silver, and by destroying them he took away their 
power of enriching themselves and rebelling against 
Rome. Whether Diocletian actually did this or not, 
it is certain that these books of a feared and prohibited 
art were subject to many another foray, as is evidenced 
by the scene recorded in the Acts of the Apostles: '^ Many 
of them which used curious arts brought their books 
together and burned them before all men: and thej^- 
counted the price of them and found it fifty thousand 
pieces of silver.'^ Such scenes were often repeated in 
the early part of the Christian era. 

The phrasing used in these writings was purposely 
so obscure that only the initiated were supposed to be 
able to understand them, and this persisted throughout 
the period of the alchemists. It sufficed not merely to 
cloak knowledge but to conceal ignorance. 

Another piece of mysticism is seen in the ascription 
of a divine origin to their art. Thus Zosimus the Panopo- 
lite claimed that the giants, sprung from the union of 
the angels with the daughters of men, were taught all 
that was supernatural and magical by their fathers and 
this wonderful knowledge was recorded in a book called 
chema. The adepts in alchemy were unanimous, however, 
in ascribing the foundation of their art to Hermes. The 
name is synonymous with Toth, the god of intellect, 
the patron of arts and sciences in ancient Egypt. As 
the god of letters, all books were dedicated to him and 
he was in one sense the author. Clement of Alexandria 



10 HISTORY OF CHEMISTRY 

describes the solemn procession in which these books 
were borne in the great ceremonies. Tin and mercury 
were set apart as metals sacred to him. During the Mid- 
dle Ages the science was often known under the name 
of the Hermetic Art, and alchemists called themselves 
Hermetic Philosophers. To close anything very securely, 
as for instance to seal it in a glass tube, is caUed 
to this day sealing it hermetically. In old times the 
symbol of Hermes was afiixed and it was thus sealed 
with '' Hermes, his seal.'' The other metals had their 
patron deities also. Thus gold was sacred to the sun, 
silver to the moon, and silver nitrate is still sold as lunar 
caustic. Copper was sacred to Venus, lead to Saturn, 
and iron to Mars; and one form of iron oxide can be 
bought on the market still as crocus martis. 

It was a custom among the early writers to ascribe 
their discoveries, books, etc., to fabulous names or an- 
cient heroes and gods. This had two objects, the first 
being to shield the true author in time of persecution 
and the second to gain a certain amount of credit and 
reputation for a discredited art by the use of the names 
of such celebrities as Moses, Solomon, Alexander, Cleo- 
patra, etc. Thus there is a treatise entitled Moses the 
Prophet on Chemical Composition. It is probable that 
such treatises were written in the early centuries of the 
Christian era. 

Manuscripts and Original Sources. — This brings 
us to inquire into the existence of any very early records. 
No original manuscript of the earliest writers on chem- 
istry or alchemy has been discovered. Our knowledge 
must be gleaned from the pages of those writing upon 
other subjects or must come from fragments handed down 



EARLY DEVELOPMENT 11 

through several copyists. The earHest manuscripts known 
are preserved in the museum at Leyden and were found 
at Thebes enclosed in the wrappings of a mummy. They 
are written partly in Greek and partly in the Demotic 
character, though they are known as the Greek papyri. 
The earUest is somewhat fragmentary, the beginning 
and the end being lost. It was written apparently about 
the third century of this era and belonged to the class 
of books burned by Diocletian. These manuscripts 
are filled with magical formulas, recipes, and descrip- 
tions of chemical processes, together with various forms 
of apparatus. Other later manuscripts are found in 
various European hbraries. 

Laws. — The next stage to be considered in the evolu- 
tion of the science is the development of laws. Man, 
with his intellectual gifts, could not rest content with 
the mere observation of facts and phenomena. Their 
orderly arrangement so that a certain uniformity or 
regularity and then a controlling law could be recognized 
was a slow process. These laws were accepted and uti- 
lized as a matter of every-day experience but their defi- 
nite statement came only with comparatively modern 
science. A stone tossed in the air returns to the ground 
and wood burned gives off certain gases along with 
heat, but it called for a Newton to state the law of grav- 
itation and not even Lavoisier could tell all the story 
of that burning and the heat. Some of the early Greek 
philosophers guessed at the indestructibihty of matter, 
but this fundamental conception played little part in 
their reasoning. 

Mutability in Nature. — It is easy to see how confus- 
ing to the early philosophers were the multiform changes 



12 HISTORY OF CHEMISTRY 

in nature. Nothing seemed lasting or stable; all was 
subject to change. The observations of one day might 
be quite overturned by those of the morrow. The Egyp- 
tians and other early peoples held this view of the chang- 
ing nature of all external objects and the absence of 
law in these changes. Observation and experimentation, 
therefore, appeared useless. As for the Greeks, Socrates 
said that the nature of external objects could be dis- 
covered by thought without observation, and the school 
of the Cynics renounced all attempts at natural science. 
It is related that one philosopher put out his eyes lest 
the sight of these changes should impair his thinking. 
Plato separated logic, as the knowledge of the immuta- 
ble, from physics, the knowledge of the mutable. That 
which was subject to indefinite change would not repay 
observing or recording. Therefore, astronomy and phys- 
ics could not be conceived of as serious objects for study 
or contemplation. There was nothing worth while to 
be learned from fields and trees and stones. 

This would seem to be folly to the modern mind, but 
it must be acknowledged that there is danger from inac- 
curate observations and undigested facts. The safety 
of the present day lies in the rigid exaction of experi- 
mental proof, a means of finding truth which these phi- 
losophers had scarcely learned to apply. There have 
been and still are deplorable looseness of statement 
and faulty logic on the part of many, even leaders of 
science. The Greek philosophers stand preeminent as 
the greatest, clearest thinkers of all time. 

Theories. — In spite of this attitude, the early phi- 
losophers made a fundamental start in searching for the 
underlying causes of the changes going on in nature 



EARLY DEVELOPMENT 13 

and the origin of the many objects seen about them. 
The theories which they advanced in explanation of 
what they observed form the last and most important 
step in the evolution which has been traced so far, and 
with these theories we have truly the beginning of science 
and the casting off of empiricism. The first question 
they sought to solve was out of what this world was 
made. While it was possible that the Greeks got some 
of their ideas from the Eg^^ptians and the}' might be 
traced to the sages of India or the Far East, the}' have 
left us the most abiding impression of their theories 
and these, in part at least, were based on observation 
and experiment. These philosophers date back to the 
sixth century before our era or earlier. 

Thus Thales of Miletus, who has been called the first of 
the natural philosophers, affirmed that water was the first 
element or principle and that out of it all things were 
made. Thus water, on heating, is changed into air and 
from air water comes. Solids are left when water is boiled 
away. This theory had its supporters even during the 
Middle Ages, some of them carefully pro\dng that plants 
would grow when fed with water onl}^ The theory 
was not completely disproved until Lavoisier showed 
the fallacy by careful experiment. When one recalls 
its universal presence and what trouble it causes the 
expert chemist of to-day to avoid entirely its presence 
in his experiments, it is easy to see how natural the con- 
clusion was that it was the universal, primal element. 

Anaximenes regarded air as the primal element; Hera- 
kleitos, fire; Pherekides, earth. According to Anaxi- 
menes, clouds were caused by the condensation of air, 
and rain by the condensation of clouds. Archelaus said 



14 HISTORY OF CHEMISTRY 

that air, when rarefied, became fire; when condensed, 
water; and water, when boiled, became air. Of course, 
the boiled natural water left solids. Empedokles intro- 
duced the idea of four distinct primal elements — earth, 
air, fire, and water — which were not interchangeable 
but formed aU things on being mixed. 

Atomic Theory. — But a further conception became 
necessary. In this mixing, what is it that is mixed or, 
as we would now express it, what is the internal struc- 
ture of these elements? Are they made up of separate 
particles? If not, how are they constituted? Long be- 
fore the time of the Greek philosophers the idea of sepa- 
rate particles seems to have been conceived in India, 
but for clear and logical thinking we must again turn 
to the Greeks. Anaxagoras of Klazomene (500 B.C.) 
was apparently the first to formulate a theory approach- 
ing the atomic. This was more clearly expressed by 
Leukippos and extended by Demokritos, who lived 
450-347 B.C. He was the founder of the atomistic 
school and Aristotle frequently cites his writings. As 
was customary for men of learning in early times, De- 
mokritos visited Egypt, Chaldea, and various parts of 
the East in search of learning, and doubtless owed much 
to the the wise men of those regions. 

Atoms. — The definition of an atom as given by De- 
mokritos was almost as definite and precise as that found 
in modern treatises. The word itseK means that which 
can not be cut or divided. There arose two schools of 
philosophers holding opposite views as to the make-up 
of the universe. The atomists maintained that it was 
made up of these indivisible particles separated by 
empty spaces (vacua). On the other hand, the plenists 



EARLY DEVELOPMENT 15 

contended for the view that matter was continuous, 
nature abhorring a vacuum. The discussion was settled 
in part by appeal to the old argument, ex nihilo nihil. 
If a particle of matter were divided until further sub- 
division was impossible, one must arrive at either some- 
thing or nothing. The latter was impossible, for out 
of nothing, nothing can be made. Hence there must be 
an indivisible remnant and this should be called an atom. 

During the Middle Ages the word lost its scientific 
significance and was adopted for small subdivisions of 
various kinds, as of time or music or anything very small 
and supposedly indivisible. Thus in general the word 
denoted a moment, a note, a sand grain, a particle of 
dust, etc. Where in the Bible we read that man was 
created out of dust one can quite properly substitute 
its synonym, atom, and so place it in full accord with 
the truth as seen through man^s study of nature. 

Ether. — The vacua of the earlier philosophers were 
filled by Aristotle with his hypothetical ether — the 
fifth element or quinta essentia. This ether is just as 
essential for the present-day explanations of natural 
phenomena and its existence is just as evasive of abso- 
lute, direct proof. Its invention at that time is perhaps 
the most marvellous achievement of the most profound 
intellect which has devoted itself to science and which 
dominated all branches of science throughout the changes 
of a millennium and a half. 

Indivisibility of the Atom. — As to the indivisibility 
of the atom in the modern theories, it may be added that 
the compound nature of the so-called elemental atom 
is well recognized. To the chemist this question of 
divisibility or indivisibility is a matter of comparative 



16 HISTORY OF CHEMISTRY 

indifference. It suffices that in all the various reac- 
tions of the laboratory the atom retains its individual 
character and may be regarded as indivisible so far as 
the usual manipulations are concerned. 

World Building. — Granted that the world was made 
of atoms, how was it put together? This problem also 
was faced and discussed by the Greek philosophers. 
It must be borne in mind that the modern meaning 
was not attached to the word element in early times 
but rather these were thought of as certain principles or 
essences which were endowed with diverse properties. 
Thus fire was warm and dry; air was warm and moist; 
water moist and cold; earth cold and dry. By mixing 
these elements various combinations and interchanges 
of properties were thought to be possible. 

According to Anaxagoras, there was at first a mixing 
of these particles of matter, the primal constituents, in 
infinite disorder or chaos. The act of creation was in 
the orderly arranging of these by a designing intelligence, 
vovs. These particles were like the masses which 
they produced when brought together and were named 
homoeomeries or like parts, and hence were not the atoms 
of atomists but corresponded to the molecules of the 
present day. The act of creation came about through 
a vortical motion which would separate these mole- 
cules and bring together those alike in size and specific 
gravity, thus building up the various substances known 
to us. This idea, of course, is drawn from the simple 
experiment of giving a rotary motion to a vessel con- 
taining finely-divided substances of different densities. 

The atomists sought to do away with the necessity 
for a desio'ning inteUigence by conceiving the indivisible 



EARLY DEVELOPMENT 17 

atoms or molecules, which were said to possess rapid 
circular motion, as falling together. These atoms were 
invisible, indivisible, solid, impenetrable, and unalterable, 
possessing no other properties except size, shape, and 
weight. They were influenced by necessity or fate, 
avayKT]. The meaning here seems to be covered by 
our word law. In falUng they had an oblique motion 
which caused atoms of like shape to collide and gather 
into masses. Of course, a vacuum or void was an es- 
sential for this theory. Aristotle pointed out that there 
could be no up nor down in mere space, no place to fall 
from and none to fall to, and hence falling was out of 
the question. If there were objects falling, they must 
fall in parallel Unes and could never meet. So Epicurus 
coined a new word to convey a new thought. This word 
meant inclination. This brought Hke particles together 
and in this we have the first suggestion of affinity. This 
idea was held also by the Hindus, who said, ^ There 
is a strong propensity which dances through every atom 
and attracts the minutest particle to some peculiar 
object.'^ This ^' propensity, ^^ however, they manifestly 
confused or identified with gravity. Aristotle regarded 
the moving ether as the motive principle. Long cen- 
turies afterwards Helmholtz proved mathematically that 
whatever the original motion was it could not have been 
set up except through the application of some exterior 
force. 

Thus in these very early times the foundations of 
experience — gathered facts, experimental testing, and 
workable hypotheses — were laid for the development 
of a true science with its attendant benefits to civiliza- 
tion. But this decided progress was all but blotted out 



18 HISTORY OF CHEMISTRY 

in the grave political changes which took place with 
the fall of the Roman Empire. 

Apparatus. — It is of interest to inquire by what 
means experimentation was carried on, and under what 
conditions, in these early centuries and for a number 
of those following. Some information as to this may 
be derived from the Greek papyri. These contain many 
drawings of alembics and other forms of apparatus 
which may of course have been later inventions if the 
great age of these papyri is disproved. The processes 
used were those requiring fire — dry methods rather 
than wet. Crucibles, furnaces, etc., abound therefore. 
There is a treatise by Zosimus on instruments and fur- 
naces in which he claims to describe the various appU- 
ances he saw in the ancient temple at Memphis. These 
were made of gold or bronze or clay. The alembic was 
a crude form of still and came from the Alexandrian pe- 
riod. The water-bath, or hain-marie as it is still called 
by the French, was said to have been invented at a very 
early period by Mary the Jewess. The blow-pipe and 
bellows both figured among these drawings as well as 
on very early Egyptian and other monuments. The 
use of glass for apparatus came much later. Jars and 
bowls of clay and other ware about complete the list. 
An investigator of the present time limited to such scant 
equipment would indeed be helpless. 



CHAPTER III 

THE DARK AGES 

The Old Order Overturned. — With the overturning 
of the Eastern Empire by the Arabians and the Western 
Empire by the Goths and Vandals one of the world's 
greatest civihzations, already decadent, was almost 
wiped out. In these troubled centuries of the Dark Ages 
few devoted themselves to literature, art, or science. 
The creative faculty was blunted and no great artist 
or philosopher was produced. But happity the hght was 
not altogether extinguished. The useful arts w^re re- 
tained and Greek learning, with its budding science, 
was transferred to Arabia and Persia. About the middle 
of the eighth centm-y there was estabhshed at Bagdad 
an academy or university which was visited by thou- 
sands of those seeking instruction. Hospitals and labora- 
tories were built and experimental science made some 
progress. Ancient books were collected and every scrap 
that could add to the store of knowledge was preserved. 
This University of Bagdad flourished for several centu- 
ries and scholars came to it from distant parts of the 
world. 

This love of learning extended to the western pos- 
sessions of the Arabians. Universities were founded 
in northern Africa and Spain. The University of Cor- 
dova, for instance, held a high reputation and was at- 
tended by many Christian students. Its library was 

19 



20 ' HISTORY OF CHEMISTRY 

said to contain 280,000 volumes. But a volume in those 
days often contained only a single stanza of a poem or 
a single chapter of a book. 

Progress Made by the Arabians. — With all their 
zeal for learning and for hoarding ancient books and 
the writing of new ones, the Arabs made little prog- 
ress in science. Centuries passed with but slight ad- 
ditions to what was already known. Nor did they give 
evidence of the clear thinking, logic, and vision of the 
Greeks. There was little worthy effort at explaining 
phenomena or advance in theory. Their chief interest 
in chemistry lay in finding or preparing new remedies 
to be apphed in the art of healing. This included the 
search for the philosophers' stone, which at first was a 
remedial agent or universal medicine. Later it became 
a supposed means of turning base metals (as lead) into 
gold. It was to this last object that the time and energy 
of the alchemists were gradually diverted. 

Transmutation of the Metals. — When it is recalled 
that the metals were not in themselves elements to the 
ancients but a ^^ bundle of properties,'' it is easy to see 
how the idea arose that one might take a common and 
dull or, as they considered it, a diseased metal and pu- 
rify or change it into one free from corruption, beauti- 
ful and valuable like gold. This delusion was a very 
early one and did much to divert the course of experi- 
mental work from its true object, the search after truth, 
to the vain chase of a will-o'-the-wisp. The tenacious 
hold of this delusion is shown by the fact that there was 
an alchemical society in France in the latter part of the 
nineteenth century, as well as alchemists in America, 
still trying to transmute lead into gold. 



THE DARK AGES 21 

The dream of transmutation was not altogether base- 
less. There was in a way experimental proof. Much 
of the lead contains gold and on prolonged treatment 
the lead disappears and gold remains. When bright 
iron is dipped into a solution of bluestone it is appar- 
ently changed into copper, for the iron disappears and 
copper takes its place. In a book attributed to an Ara- 
bian alchemist of the eight century called Geber we read: 
^Tn copper mines we see a certain water which flows 
out and carries with it thin scales of copper which by a 
long-continued course it washes and cleanses. But after 
such water ceases to flow, we find these thin scales with 
the dry sand in three years to be digested with the heat 
of the sun; and among these scales the purest gold is 
found; therefore, we judge those scales were cleansed 
by the benefit of the water but were equally digested 
by the heat of the sun, in the dryness of the sand and so 
brought to equahty.'' Very plausible reasoning from 
defective premises, as Thomson observes. 

Geber. — Geber considered all metals to be compounds 
of mercury and sulphur in varying proportions, an opin- 
ion which he said he derived from the ancients and which 
was handed down with variations through the Middle 
Ages. His observations on sulphur show the advances 
made and the limitations of the time. ^'Sulphur,'' he 
writes, ^^ is a substance, homogeneous and of a very strong 
composition. Although it is a fatty substance, it is not 
possible to distil its oil from it. It is lost on calcining. 
It is volatile like a spirit. Every metal calcined with 
sulphur augments its weight in a palpable manner. 
All the metals can be combined with this body except 
gold, which combines with it with difficulty. Mercury 



22 HISTORY OF CHEMISTRY 

produces with sulphur by way of sublimation cinna- 
bar. Sulphur generally blackens the metals. It does 
not change mercury into gold nor into silver as has been 
imagined by some philosophers.'^ 

Glass was by this time included in the materials used 
for apparatus and the process of distillation was prac- 
ticed. The product was called a spirit, as spirit of wine, 
etc. Geber understood the purification of substances 
by crystallization, solution, and filtration. The latter 
process was known as distillation through a filter. The 
majority of the processes in use up to the eighteenth 
century were known to him. 

New Substances. — The alkaline substances were 
known at the time of Geber and caustic soda was pre- 
pared. Saltpeter and sal ammoniac or ammonium chlo- 
ride were also known, as well as the mineral acids, nitric, 
sulphuric, and aqua regia. These were used as solvents 
and thus the wet processes of modern chemistry began 
to substitute the dry processes of the furnaces. Various 
sulphates, or vitriols as they were called, were spoken of 
and also borax and purified common salt. Certain com- 
pounds of mercury, as corrosive sublimate and the red 
oxide, were also used. As an illustration of these proc- 
esses, we may take the method of preparing silver ni- 
trate which Geber discovered: ''Dissolve silver calcined 
in solutive water (nitric acid); which being done, heat 
it in a phial with a long neck, the orifice of which must 
be left unstopped, for one day only, until a third part 
of the water be consumed. This being effected, set it 
with its vessel in a cold place and then it is converted 
into small fusible stones like crystal. '^ 

Further addition to knowledge was very limited until 



THE DARK AGES 23 

the thirteenth and fourteenth centuries. The decadence 
of Moorish power in Europe was rapid. The Arabs were 
driven from Spain, and Bagdad was conquered by the 
Mongols. Still for some centuries the influence of Arabic 
thought was gi^eat. Theu writings were translated into 
Latin and other languages and formed the chief treasure 
of medical and scientific workers^ and their modes of 
thought and work were often imitated by their monkish 
successors. Schools and universities were estabhshed 
at MontpelHer, Paris, Naples, Padua, and other places, 
and the center of learning shifted westward and north- 
ward. 



CHAPTER IV 

THE MIDDLE AGES 

During the previous centuries of intellectual steril- 
ity in Europe the monks had been the only conserva- 
tors of books and scientific works — a dead treasure 
in their hands. These orders began to awaken to intel- 
lectual life and to labor for the spread of knowledge. 
The crusaders brought various industries to Europe 
from the East. The gold-making craze spread and there 
was much talk of magic. These met with inquisito- 
rial opposition on the part of the church, which indeed 
held a close control over all progress in knowledge or 
introduction of new ideas. The only noted scientific 
workers of the early part of this period came from the 
monkish orders. 

Albertus Magnus (1193-1280). — Thus Albertus Mag- 
nus was Bishop of Regensburg. His lectures were at- 
tended by thousands of students and he wrote a number 
of books. He introduced the word affinity to designate 
the cause of the combination of the metals with sulphur. 

Roger Bacon (1214-1294). — Roger Bacon was the 
most remarkable man of this time. He was a Francis- 
can friar in England and was persecuted for his alleged 
dealing with magic, spending some ten years in prison, 
though he had written a book to prove that there could 
be no such thing as magic. He was an astronomer, 
mathematician, physicist, and alchemist. He was the 

24 



THE MIDDLE AGES 25 

first to draw attention to the error in the Juhan cal- 
endar. It was his success as a mechanic in the produc- 
tion of several automata which brought him the repu- 
tation of being in league with the devil. He seems to 
have known how to make gimpowder and it was first used 
by the Enghsh at the battle of Crecy some fifty years 
after his death. He is reputed to have been the inventor 
of the telescope, camera obscura, and burning lenses. He 
subjected organic substances to dry distillation and noted 
the inflarmnable gases given off. Some one during this 
period by distillation of bones obtained what was called 
spirit of hartshorn and thus ammonia was discovered. 
Also wine was distilled and spirit of wine or alcohol 
obtained. These were about all of the practical gains 
in the three centuries preceding the sixteenth. 

Changes in the 16th Century. — In the sixteenth cen- 
tury began a period of restless adventure and discovery, 
together with a throwing off of the cramping bonds of 
authority. Just before the dawn of the century America 
was discovered and men were exploring its mlds. The 
discoveries of Copernicus as to the stellar system and 
the Reformation of Luther fall in this age. The art of 
printing was developed by Gutenberg. Books became 
more plentiful and about eighty universities in Europe 
were giving a meagre training to thousands of students. 
There was a tendency to unite chemistry and medicine. 
Life processes began to be accounted for on chemical 
grounds, and medicine was in a measure a branch of 
applied chemistry and then began to be looked upon 
as the true aim and end of chemistry. In consequence 
laboratory work was more carefully carried out and new 
compounds were discovered. A new object and zest were 



26 HISTORY OF CHEMISTRY 

given to the study and chemistry became the pursuit 
of trained scholars. 

Paracelsus (1493-1541). — One of the noted men of 
this century was Paracelsus. He taught at the Uni- 
versity of Basel, covering the subjects of medicine, chem- 
istry, and pharmacy. His great service lay in breaking 
away from the ancient authorities, such as Galen, Hip- 
pocrates, and Aristotle, insisting that instruction should 
be given and books written in the language of the people 
so as to be easily intelHgible to them, and stressing the 
importance of gathering knowledge through experiment 
and from every first-hand soiu^ce. As a physician, he 
was skillful and successful and substituted for the old 
theory of disease (that it came from excess in either bile, 
phlegm, or blood) a new one that each disease has its 
own definite cause and sequences and must be antago- 
nized by specific remedies. This marked the inaugura- 
tion of the modern method of antagonizing disease. 

As a chemist he added much to the previously known 
analytical methods and the partial discovery of hydrogen 
is accredited to him, though its distinctive separation 
and identification were lacking. He laid the foundation 
for a classification of the metals which lasted for several 
generations and he was largely instrumental in turning 
chemistry from wasteful aims into a most useful adjunct 
to medicine. Pharmacy as a distinct profession and ob- 
ject of study was largely founded by him and he intro- 
duced many new and valuable remedies. Mercurial 
preparations, lead compounds, iron salts, arsenic for 
skin diseases, milk of sulphur, bluestone, and others 
might be mentioned. Various plant remedies had been 
in use as decoctions or simply sweetened with sugar. 



THE MIDDLE AGES 27 

He began the search after theu* active principles and 
brought them into use as tinctures, essences, and extracts. 
Tincture of opium, for instance, was first used by him 
and given its present name laudanimi. 

Agricola (1494-1555). — Contemporaneous with Para- 
celsus but forming a strong contrast to him was the tech- 
nical chemist, Agricola. He was born in Germany and 
studied at Leipsic, and was the first and for a long time 
the only one to devote his scientific knowledge to the 
improvement of metallurgy and the industrial arts. His 
chief work is called De Re Metallica and is a connected 
treatise on metallurgy. This book went through many 
editions and was for a long time considered an authority 
on the subject, substituting scientific theories for the 
persistent ancient beHefs that metals grew in the mines 
in some such way as vegetables grew in the surface soil, 
that if a mine were closed and allowed to stand the metal 
would grow again, and that one metal might be made 
from another. In his book is given a clear account of 
the condition of the various industries of his day and the 
different methods and operations then in use. Agricola 
was a physician as well as technical chemist but he did 
not attribute disease and growth to the metals. 

Van Hehnont (1577-1644). — Two more of these 
physician-chemists deserve mention, both belonging to 
the seventeenth century. The first was Van Helmont, 
a Belgian, who studied at the University of Louvain. 
Most of his life was spent at work in his private laboratory 
and from this time on we find that in such laboratories 
most of the real progress was made. He took up the 
old-world theory that water was the primal element and 
in support of it advanced many ingenious arguments 



28 HISTORY OF CHEMISTRY 

from plants and animals. He performed the famous 
experiment of the willow and it is the most plausible among 
his experiments adduced as proofs of his theory. 

A large earthen vessel was filled with two hundred 
pounds of dried earth and a willow weighing five pounds' 
was planted in it. This was duly watered with rain and 
distilled water. After five years the willow was pulled 
up and found to weigh one hundred and sixty-nine pounds 
and four ounces. The earth had decreased two ounces 
in weight. Thus, according to Van Helmont's reasoning, 
one hundred and sixty-four pounds of root, bark, leaves, 
etc., were produced from water alone. Fish also, he 
said, live on water and yet contain all the peculiar animal 
substances. These are then made from water. 

He introduced the term gas to distinguish water vapor 
and other elastic fluids from air and was the first to study 
these substances systematically. The vapor coming from 
fermenting substances, or carbon dioxide, he called gas 
sylvestre. He divided gases into those which were in- 
flammable and those which were not. As he was ignorant 
of any method of collecting and separating them, his 
knowledge was very imperfect. He believed in curing 
diseases by dietetics, by working on the imagination, 
use of incantations, etc. Still he made use of chemical 
preparations and greatly advanced them in popular 
favor. At the same time he was an enthusiastic mystic, 
believing in the transmutation of metals and in magic. 
Mice, he thought, could be made by placing a soiled shirt 
with some flour in a barrel. It may be safely stated that 
at least this would be one way of collecting them. 

Glauber (1604-1668). — A more distinguished name is 
that of Glauber, a German, whose skill was devoted to 



1 



THE MIDDLE AGES 29 

increasing the knowledge of chemical substances. He dis- 
covered and introduced many new chemical preparations. 
Purer and stronger hydrochloric and nitric acids were 
prepared by him. He prepared sodium sulphate, to which 
he ascribed remarkable curative powers, calKng it sal 
mirdbile. It has for a long time been known as Glauber^s 
salt. Various other sulphates and chlorides were pre- 
pared by him. He used the method of double decom- 
position in his preparations and thus described it: ^^Aqua 
regia which has taken gold into solution kills the salt 
of tartar (potash) of the liquor of flints (silicate of potash) 
in such way as to cause it to abandon the silica, and in 
exchange the salt of tartar paralyzes the action of the 
aqua regia in such way as to make it let go the gold which 
it had dissolved. It is thus that the silica and gold are 
both deprived of their solvents. The precipitate is com- 
posed, then, at the same time of the gold and of the sihca, 
the weights of which together represent that of the gold 
and of the silica originally employed.'' His appeal to 
the balance for accuracy and as confirming his theory is 
noteworthy. 

Two mistakes were made by these physicians and iatro- 
chemists, as they were called. They attempted to ex- 
plain on chemical principles all the changes and processes 
going on in the body. This was certainly not possible 
with the deficient knowledge of the day. To Van Helmont, 
for instance, disease consisted in the excess or preponder- 
ance of base or acid in the body juices. Secondly, too 
narrow a limit was set to chemistry. It was destined to 
fill a much larger sphere than that of an adjunct to any 
other science. 

The Rise of Theory. — The science did not remain 



30 HISTORY OF CHEMISTRY 

long m this subordinate position. It so grew in extent 
and importance that it was able to burst the bonds of 
too close an alliance with medicine and to take for its 
field the study of the combinations and decompositions 
of all known substances. The inductive philosophy of 
Francis Bacon began to have effect and chemistry as- 
sumed its place among the sciences. Its study was no 
longer obscured by gold-hunting nor Hmited to the prep- 
aration of medicines. There came a period of quahtative 
chemistry, a step toward the higher quantitative work 
and a great step forward from the haphazard chemistry 
of the past. There are dangers in relying upon quali- 
tative tests alone and mistakes were made. For a while 
the guiding principle seems to have been the old saying 
that similar appearances are due to similar causes, a 
saying which has much plausibility and yet might lead 
to error. Minerals were analyzed and new substances 
discovered. Some synthetic work was done and new 
compounds formed. There was a growing desire to know 
something of the underlying causes, to understand better 
the phenomena observed, and to find explanations for 
them. Processes in the laboratory became more frequently 
those of the ^'wet way'' where solutions were concerned. 
To insure accuracy and assist judgment more frequent 
use was made of the balance and there was a return to 
logic and philosophy as in the time of the Greeks. And 
so the progress made in the seventeenth century far 
exceeded that of all the previous centuries. 

Robert Boyle (1626-1691). — First among those to 
pursue the study of chemistry from a noble desire for 
a deeper insight into the workings of nature was Robert 
Boyle. He was born in Ireland, lived at Oxford, and aided 



THE MIDDLE AGES 31 

in founding the Royal Society of England/ He antago- 
nized the alchemists, except in respect to a belief in the 
possible transmutation of the metals, and also contended 
with the views of Van Helmont, though he agreed that 
one must look to chemistry for the solution of the greatest 
problems of medicine. He was the first to apply Bacon's 
inductive method to the science and maintained that 
experiment alone was the proper basis for theory and that 
all theories must be tested by experiment. Before at- 
tempting any theorizing as to explanations he went to 
work to correct the faulty experiments and imperfect 
observations of the past and thus to clear the path for 
an understanding of the phenomena. 

Experiments upon Air. — Boyle's experiments were 
largely upon air and water, choosing two of the common- 
est and yet most instructive substances in nature. The 
knowledge of the first, physically and chemically, was 
greatly advanced by him. He made use of an improved 
air-pump and examined the behavior of different sub- 
stances in a vacuum. He enunciated the law of pres- 
sure for gases, namely, that the volume of a gas varies 
inversely as the pressure. This is still known as Boyle's 
Law. Experiments were carried out also as to the 
height, weight, and density of the atmosphere. Further- 
more, he showed that something in the air was consumed 
by breathing or by the burning of a substance in it. This 
was, of course, only a verification of observations made 
long before. He proved that an increase in weight was 
caused by calcination and that the calx was specifically 
fighter than the original metal. The calcination of such 
a substance as lead, he showed, consumed air. It is 
strange how near his experiments brought him to impor- 



32 HISTORY OF CHEMISTRY 

tant truths. But he was not always happy in the inter- 
pretation of his results. He could see many faults in the 
theories of the times but seldom saw his way clear to 
estabUshing a theory of his own. 

Constitution of Matter. — In studying the nature of 
the various substances known to him Boyle devised a 
system of qualitative analysis, arranging these substances 
into classes and groups. Vegetable coloring matters were 
used by him as indicators for acids and bases. Regular 
reagents were introduced by him with directions for 
their use. Many of his tests we make use of at the present 
day as, for instance, ammonia was driven out of its com- 
pounds by lime or caustic potash and tested for by its 
fuming with h^^drochloric acid. His ideas as to the con- 
stitution of matter were much like those of the present. 
He considered all bodies to consist of very small particles 
and beheved that the union of these particles gave com- 
pounds. Decomposition was impossible until the attrac- 
tion between the particles had been overcome. Accord- 
ing to this hypothesis, the differences between bodies 
were due to the inequaUties in the form, structure, and 
movement of the particles. In his opinion one or two 
primal elements would suffice to explain all the varieties 
of substances in nature. This comes rather close to the 
hydrogen-helium hypothesis of the present. And yet 
when he came to apply his hypothesis his limitations 
became very apparent. The particles of water, he sup- 
posed, might under certain conditions be so grouped and 
set in motion as to form the substance which we know as 
air. It is easy to see that all through the ages one of the 
great puzzles set for thinking men has been the invisible 
atmosphere surrounding us, forming and buoying up its 



THE MIDDLE AGES 33 

cloud masses and pouring down its floods of water, hail, 
or snow. 

In defining a chemical compound as one formed by the 
imion of two or more components which lose their prop- 
erties, the compound having new and different properties, 
Boyle distinctly placed himseK on the plane of the modern 
chemist. Differences in affinity were also recognized by 
him in preparing tables giving the relative affinity of 
various metals towards the acids. Several chemists 
busied themselves with such Usts in later years. 



CHAPTER V 

THE CHEMISTRY OF COMBUSTION 

The most important reaction in chemistry is that of 
oxidation, known in its common, everyday occurrence 
as combustion. A rational and satisfactory explanation 
of this process was therefore a fundamental necessity 
for the progress of the science. Some progress might be 
attained under a false theory but there would be many 
misconceptions and errors. The theory of combustion 
which prevailed through most of the eighteenth century 
was called the phlogiston theory. This theory was 
first imperfectly stated by Becher in the latter part of 
the seventeenth century but was more clearly given by 
Stahl, who introduced the term phlogiston, or fire sub- 
stance. Both of these were German chemists. Since 
the theory was false, it obscured or twisted facts and 
necessarily retarded progress. 

Phlogiston Theory. — The theory may be briefly stated 
as follows. The purpose was to explain the changes 
which occur when a metal is heated in the air and changed 
into a powder. The metal was said to be calcined and the 
resulting powder was called a calx. Of course the burn- 
ing of wood or coal with the formation of ashes and many 
similar operations come under the same heading. Ac- 
cording to the phlogistics, as they were called, the metals 
lost something which was the hypothetical phlogiston and 
the calx remained. The metal, then, was a compound 

34 



THE CHEMISTRY OF COMBUSTION 35 

made up of calx and phlogiston. This phlogiston was 
present in all combustible substances as coal, inflam- 
mable gases, etc., and some substances contained more 
than others. The supposed proof of the theory lay in 
the fact that when a metallic calx was heated with a 
substance rich in phlogiston, such as coal, the metal 
could be restored. Thus, when iron was heated in the 
air a red calx was formed, copper gave a black calx, and 
metalhc iron or copper could be recovered by heating 
these with coal. 

The question was asked: What is this phlogiston and 
why can no one get hold of it to examine it? Wild and 
absurd conjectures were made as to its nature, some of 
these placing it beyond experimental evidence. Again 
the question of weight relations arose, thus appealing to 
the balance, and it was found that the calx weighed more 
than the original metal. How could that be possible 
if the metal had lost something? The explanation offered 
as to this was that when wood was burned the flame 
ascended and hence the fire substance, or phlogiston, 
possessed levity rather than gravity and when combined 
in substances made them hghter. The trouble was that 
the discussion became one of logic with neglect or dis- 
regard of facts. One of the last of the phlogistics was 
Priestley, who argued stubbornly in behaK of his views 
until his death in 1804. 

Composition of Air. — One of the causes of the failure 
to recognize the true explanation of combustion was 
ignorance as to the composition of the air which was 
essential to all combustions. Of course the necessity for 
air in burning anything had been recognized in very early 
times. The phlogistics explained this by maintaining 



36 HISTORY OF CHEMISTRY 

that phlogiston could not escape unless combined with 
air. Animals breathing in air were supposed to breathe 
out phlogiston. 

Hooke's Theory of Combustion. — During the latter 
half of the eighteenth century there were three dis- 
tinguished chemists in England, all of them adherents of 
the phlogiston theory and its earnest defenders. These 
were Black, Cavendish, and Priestley. They were either 
in ignorance of or attached no importance to the theory 
of Hooke, their fellow countryman, as to combustion. 
This theory, pubhshed in 1665 in his Micographia, 
claimed to be based upon experiment. It is contained 
in twelve propositions but may be briefly stated as follows: 
Air supports combustion but this combustion will take 
place only after the substance has been sufl&ciently heated. 
There is no such thing as elemental fire. This combustion 
is caused by a substance inherent in and mixed with the 
air which is very much Hke, if not the very same as that 
which is fixed in saltpeter. Mayow a little later recog- 
nized that the air contains a substance which unites 
with metals when they are calcined. This substance will 
also change venous blood to arterial, as shown by the 
color. It is contained in saltpeter, for substances burn 
when mixed with saltpeter. He therefore called this 
component of the air spiritus nitro-aerius. 

It was the discovery of oxygen that struck the death 
blow to the phlogiston theory. Strange to say it was 
discovered and identified in 1774 by Priestley and inde- 
pendently by Scheele, both of them phlogistics, who 
failed to grasp its bearing upon the phlogiston theory. 
In the hands of Lavoisier, the great Frenchman, it revealed 
the secret of combustion. Priestley visited Paris and 



THE CHEMISTRY OF COMBUSTION 37 

showed Lavoisier how to prepare it by first heating mer- 
cury in the air until the red precipitate was formed. 
When this was placed under a bell-jar from which the 
air had been pumped and was heated, the original mercury 
was regained with hberation of a gas which would support 
combustion. By weighing the mercury, then the red 
precipitate and the gas given ofE, it was shown by Lavoisier 
that the increase in weight of the mercury in forming 
the red precipitate or calx corresponded with the weight 
of gas which was taken up by it. Lavoisier called this 
gas oxygen or the acid-producer. Priestley called it de- 
phlogisticated air. The discovery of hydrogen by Cav- 
endish and the fact that on burning it formed water 
completed the proof of the new theory that combustion is 
simply combining with oxygen or oxidation. Cavendish 
called this gas inflammable air but Lavoisier named it 
hydrogen or the water-former. 



CHAPTER VI 

THE NEW CHEMISTRY 

It is manifest from the preceding pages that chemistry- 
was now developing into a science. The gathering of 
facts was going on apace. The chief lack was a rational 
system of arrangement based on the distinctive charac- 
teristics of the substances involved. A distinction had 
already been drawn between compounds and elements. 
An element was a simple body made up of just one kind 
of matter. For instance, no lighter nor heavier substance 
could be got from it. A compound was made up of two 
or more different substances. Since the term element 
was still in great measure reserved for the four primal 
principles of the Greeks, what we now call elements were 
spoken of as simple bodies. The finding of new elements 
and compounds now depended upon analytical results. 

Analysis. — Tests for the elements had to be devised 
depending upon their specific properties. To simplify 
the work these tests must be systematically arranged. 
Analysis in the wet way was first outlined by Boyle and 
chiefly appUed to mineral waters, which attracted much 
interest and investigation. Bergman (1735-1784), a 
Swedish chemist and professor at the University of 
Upsala, enlarged the number of reagents and studied 
their action on such substances as occur most commonly. 
This branch of the science then began to be exact . In quan- 
titative analysis, also, he took an important step forward 

88 



THE NEW CHEMISTRY 39 

in abandoning the plan of actually isolating the various 
constituents and introduced the method of transform- 
ing each constituent into some compound whose exact 
composition was known and which could be easily iso- 
lated. Sometimes the composition was unknown and the 
simple body present had never been separated, as siUca 
or alumina, and in such cases the analyst had to content 
himseK with separating the compound which was to him, 
for all intents and purposes, a simple body. Bergman 
analyzed a large nimiber of minerals and other substances. 
For those which he could not dissolve in water or acids 
he introduced the method of fusion with caustic or car- 
bonated alkalies so as to bring them into solution, a most 
important addition to analytical methods. Some of his 
researches were masterly and quite in the spirit of the 
present time. Such, for example, was his work on the 
differences between wrought iron, steel, and cast iron; 
also upon the cause of ^^cold shortage'' in iron. Sweden 
produced much iron and this made the work of Bergman 
especially important for his native land. He also analyzed 
the air and reported: ^^ Common air is a mixture of three 
elastic fluids; free aerial acid (carbonic acid) but in such 
small quantities that it does not sensibly alter the color of 
litmus; an air which can neither serve for combustion nor 
for the respiration of animals, which, therefore, we call 
vitiated air until we know its nature perfectly; and lastly 
an air absolutely necessary for fire and for animal life 
which forms pretty nearly the fourth part of common air 
and which I regard as pure air.'' In this he was the first to 
give a clear statement as to the quantitative composition 
of air. This was based on his own and on Scheele's 
experiments. 



40 HISTORY OF CHEMISTRY 

Scheele (1742-1786). — Probably no one before nor 
since his day has made so man^^ important discoveries 
as Scheele, a fellow countryman of Bergman. He was 
a pharmacist, poor and reserved, and yet out of his 
poverty and imperfect appliances achieved wonderful 
success in mastering nature's secrets in his short life 
of forty-three years. His letters have been published in 
modern times and they reveal how much he knew and how 
far he was ahead of his contemporaries. His first work 
was upon the organic acids, many of which he isolated 
and examined. Among organic acids he discovered tar- 
taric, oxahc, malic, citric, and gallic; among inorganic, 
molybdic, tungstic, and arsenic. Three elements were 
discovered by him, oxygen, manganese, and chlorine; 
and one new alkaline earth, baryta. He prepared oxygen 
by heating manganese dioxide in the same year that 
Priestley prepared it from mercuric oxide. His chief de- 
ficiency lay in the matter of understanding phenomena 
and formulating theories. It is evident that his acceptance 
of the phlogiston theory led him astray in this. 

Analysis of Air. — Scheele examined the atmosphere 
with a view to determining what part it plaj^ed in the 
phenomena of combustion. First, he tried the action of 
various substances upon the air. These substances were 
supposed to contain phlogiston and hence, he reasoned, 
would give it off to the air held in a closed space. Some 
of the substances experimented upon were moist iron 
filings, fresh moist iron hydroxide, etc. He observed that 
the air diminished in amount and that the portion left 
was incapable of supporting combustion. This diminu- 
tion of volume he thought was due to an absorption of 
phlogiston by the air, and hence the air should be specifi- 



THE NEW CHEMISTRY 41 

cally heavier. To his surprise he found the opposite to 
be true. A part of the air had disappeared and the 
remainder was specifically lighter. Scheele concluded 
that the atmosphere consisted of two different kinds of 
air — one having no power of taking up phlogiston and 
hence being left behind in combustions, the other taking 
up phlogiston in an enhanced degree. This was his fire- 
air, or Lavoisier's oxygen, though as yet unknown to the 
great French chemist. His experiments as to the relative 
proportions of these two constituents fall far behind in 
accuracy those made a little later by Cavendish. He 
pursued his investigation further and was badly misled 
by the phlogiston fancy. Thus, in explanation of the 
experiment just described, he concluded that the union 
of phlogiston with one part of the air caused a diminution 
in volume because a tenuous, delicate substance had been 
formed and this escaped through the pores of the glass 
vessel. This delicate substance was, in his opinion, 
fire or heat. Fire then was a compound of fire-air and 
phlogiston. This fire or heat he believed could be de- 
composed into its constituents by the use of such sub- 
stances as would combine with the phlogiston and set 
the fire-air free. He thought he could do this with nitric 
acid. He distilled niter and oil of vitriol, or sulphuric 
acid, and obtained nitric acid and a gas which supported 
combustion better than the air itself. This supposed 
decomposition of heat he effected further by heating other 
substances as manganese dioxide and niter. Thus he 
isolated oxygen or fire-air, as he called it. 

Boerhaave (1668-1738). — There was in Holland at 
this time a very influential chemist named Boerhaave, 
who was a professor at the University of Leyden and who 



42 HISTORY OF CHEMISTRY 

did much to clear the way for the new chemistry by ex- 
posing the errors of the alchemists and their successors 
and the falsity of their views. He tested with care and 
accuracy everything that he taught, and spared neither 
pains nor time to have his observations correct. For 
instance, the alchemists maintained that mercury could 
be fixed in the form of a fireproof metal without the 
addition of any other substance. Boerhaave kept mercury j 
at a somewhat raised temperature in an open vessel for j 
fifteen years without noting any change. So, too, when < 
heated higher in a closed vessel for six months no change ! 
could be detected. It had also been maintained that if i 
mercury were repeatedly distilled, a more volatile essence 
with peculiar properties could be obtained. Boerhaave ! 
carried out this distillation five hundred times without \ 
securing the essence. His skill in interpreting facts and '■ 
the clearness of his theoretical views made him an excellent ; 
teacher, and his text-book on chemistry went through re- 
peated editions and translations into other languages and , 
was used for many years after his death. He seemed to | 
take Httle notice of the phlogiston theory. , 

Fixity of proportions. — It is noteworthy that another 
foundation stone was being laid without discussion or ; 
statement, and that was in the general acceptance of \ 
the essential conception that the constituents of each 
definite compound were always in the same definite pro- \ 
portion. This grew naturally out of the experience of 
the analytical chemist who tested the quantitative re- \ 
lations with his balance. If these proportions were | 
not fixed his anal3rtical work was futile. No question ^ 
was raised concerning this until the close of the century. ! 

Berthollet (1748-1822). — About the beginning of j 



THE NEW CHEMISTRY 43 

the nineteenth century the question was taken up by 
BerthoUet, one of the first and ablest of Lavoisier's sup- 
porters. He contended that these proportions were 
not constant but that the relative masses of the combin- 
ing substances determined the proportions in which 
they would unite to form compounds. His views met 
with immediate opposition on the part of leading chem- 
ists and gave a new direction to their investigations. 
His chief antagonist was his fellow countryman, Proust, 
and the exact quantitative composition of many com- 
pounds was worked out. In the course of these investi- 
gations it was foimd that metals might have several 
oxides and also that hydroxides existed. The victory 
finally remained with Proust. This problem has arisen 
in subsequent years as analytical methods improved 
greatly in exactness, but the definiteness of proportions 
seems established. 

Views as to AflSnity. — Several chemists had turned 
their attention to the attractive force which brought 
about combination between different substances and 
held together the different particles in a compound. 
The name affinity had been given early to this combin- 
ing force. While there was no measure for this force nor 
theorizing as to its nature, several chemists endeavored 
to settle the relative strength of attraction between 
different substances and constructed what were called 
affinity tables. The question comes down to this: WTiich 
metal, iron or copper or lead, has the greatest affinity 
for sulphur; or which acid has the greatest affinity for 
soda? Such tables were helpful in those times but failure 
to recognize the influence of other factors made them of 
shght scientific value. Bergman's table was one of the 



44 HISTORY OF CHEMISTRY 

best of these early efforts, since it shows a knowledge 
that affinity phenomena depend upon the temperature 
and physical state. 

Relative Affinity for Sulphuric Acid 



Wet Way 


Dry Way 


Baryta 


Phlogiston 


Potash and soda 


Baryta 


Ammonia 


Potash 


Alumina 


Soda 


Zinc oxide 


Lime 


Iron oxide 


Magnesia 


Copper oxide 


Metallic oxides 


Mercury oxide 


Ammonia 


Silver oxide 


Alumina 



Berthollet has exerted a lasting influence upon the 
views concerning affinity and showed in high degree 
the power of abstract conception and logical develop- 
ment of chemical ideas. He reasoned that affinity was 
by no means a simple force and easy to determine and 
measure, but was influenced by temperature, physical 
state, cohesion, and especially by mass. The latter largely 
determined the course of chemical reactions. Thus rock 
made up of the hardest sihcates is weathered or grad- 
ually decomposed by the action of rain containing one 
of the weakest of acids, carbonic acid. 

Lavoisier (1743-1794). — The materials were now 
gathered and the architect and builder was at hand. 
Lavoisier has justly been called the Father of Modern 
Chemistry. Born in Paris, carefully educated, gifted 
in intellect, accurate in work, and with a clear, far-seeing 
vision, he was one of that type which is born now and 
then in time of need to point out the path for succeed- 



THE NEW CHEMISTRY 45 

ing generations. There may be many priests in the 
temple of science but only at long intervals does a pro- 
phet arise. At the early age of twenty-one he was awarded 
a medal by the government for a memoir upon the best 
and most economical method of lighting the streets 
of a city, and at twenty-five he was chosen an adjunct 
member of the French Academy. Chemistry did not 
receive the whole of his attention at first but shared it 
with geology, mineralogy, and mathematics. The re- 
markable discoveries which were being made in chemistry, 
especially in connection with gases and the atmosphere, 
drew him, however, to devote all his energies to chem- 
istry. For more than twenty years he was indefatigable 
as a worker, repeating the experiments of others and 
pursuing fresh lines of inquiry. And then his life and 
activities were cut short by the coming on of the French 
Revolution. He was executed by Robespierre in 1794 
at the age of fifty-one. 

Character of his work. — Lavoisier's most valuable 
services were as an interpreter of his own work and that 
of others. He showed a clear insight into the causes of 
phenomena, a quick perception of the importance of the 
many discoveries of his time, and a comprehensive grasp 
of facts and their inter-relation and connection. These 
powers enabled him to detect the errors and falsity 
in the theory and reasoning of the chemists of his age 
and to lay the basis for the new chemistry of the quan- 
titative era. Exclusive importance had been attached 
hitherto to visible phenomena, whereas he introduced 
a deeper study of chemical reactions and the relations 
of quantity. 

Experiments on Combustion. — In 1774 he pubhshed 



46 HISTORY OF CHEMISTRY 

his first strictly scientific volume under the title : Essays 
Physical and Chemical, In this he described all that 
had been done on the subject of gases from the time 
of Paracelsus down through the work. of Priestley. He 
also gave an account of his own experiments. He showed 
that when metals were calcined their weights increased 
and that a portion of air, equal to their increase in weight, 
had been absorbed from the surrounding atmosphere. 
He burned phosphorus in the air and observed the 
decrease in the volume of the air and the increase 
in the weight of the phosphorus. We are apt to think 
that the mere proof that the metallic calx weighed more 
than the metal was sufficient to disprove the phlogiston 
theory. Both parts of the proof given by Lavoisier were 
necessary and even then he felt it to be insufficient and 
merely preliminary to his final work. It had already 
been shown that the calces were heavier than the metals 
from which they came and that they were specifically 
lighter, but the phlogistic chemists had disregarded 
these weight relations, taking refuge in the hypothesis 
of a phlogiston unaffected by gravity or actually making 
substances hghter by its presence. 

Composition of the Atmosphere. — In Lavoisier's 
further attack upon the phlogiston theory he examined 
the atmosphere and its constituents. In the book men- 
tioned above he tells nothing to indicate that he knew 
the composition of the air or the distinct nature of oxy- 
gen. These were discoveries reserved for Scheele and 
Priestley, but Lavoisier was evidently very near to 
their discovery and was only anticipated in this. When 
Priestley visited him shortly afterwards and showed 
him how to prepare oxygen from the red oxide of mer- 



THE NEW CHEMISTRY 47 

cury, Lavoisier immediately saw what the discovery 
meant and how it made plain much that was unexplained 
in his own work. It altered his views and suggested to 
him the nature of atmospheric air and of the changes 
taking place in the calcination of the metals. For twelve 
years he worked over these problems, performing a great 
number of experiments with an accuracy hitherto un- 
known. He then boldly proclaimed the non-existence 
of phlogiston and replaced this old theory by a new one, 
explaining the phenomena of combustion and reduc- 
tion as due to the combination with oxygen or its separa- 
tion. He first won to his views the distinguished French 
chemists of his day, and before many years all men of 
standing in the science gave in their adherence to the 
new explanation offered by him, except a few who could 
not give up views which had formed the basis of all 
their scientific work. The year 1786 may be fixed as the 
date of the overturning of the old theory. 



CHAPTER VII 

THE FOUNDATIONS 

Composition of Water. — Lavoisier's triumph over 
the supporters of the phlogiston theory was complete 
when he made public his researches upon the composi- 
tion of water. The hydrogen evolved when a metal 
was acted upon by an acid was considered at first by some 
to be identical with the hypothetical phlogiston and 
Cavendish, the discoverer of hydrogen, maintained this 
view to the end of his life. When Cavendish's further 
discovery of the formation of water by the burning 
of hydrogen was told to him Lavoisier saw his way to 
solution of this puzzle and lost no time in repeating so 
important an experiment. The explanation he offered 
to the reaction between the acid and the metal was 
that the hydrogen came from the water, which took part 
in the reaction; at the same time the oxygen combined 
with the metal and thus it was not the metal but the 
metallic oxide which was dissolved by the acid. In other 
cases, as in the action of nitric acid upon copper, the 
metal decomposed the acid and not the water, taking 
oxygen from it to form an oxide, and this was dis- 
solved by the remainder of the acid. The deoxidized part 
of the acid, he said, escaped as a gas. A prophet in chem- 
istry is not inspired and can only do his best with such 
facts as are known to him. Hence one must be lenient as 
to the instances in which these views fail of the full truth. 

48 



THE FOUNDATIONS 49 

Transmutation of Water. — One of Lavoisier's early 
investigations bore upon the nature of water and well 
illustrates his accuracy, thoroughness, and acute reason- 
ing. It had been noted by many earlier investigators 
that when pure water was boiled for a long time in a 
glass vessel a white residue was found in the vessel after 
evaporation. This was long regarded as a conclusive 
proof that water could be changed into earth. Appeal- 
ing to the balance as arbiter, he first weighed his glass 
vessel and then, after heating pure water in it for one 
hundred days, found there was no change in the weight 
of the vessel and its contents; that is, the vessel and 
the water weighed the same after the heating as before. 
When the water was removed the vessel weighed less than 
the original weight of the empty vessel. When he evap- 
orated the water he obtained a residue which he found 
corresponded in weight to the loss in weight of the empty 
vessel. He, therefore, concluded that water on being 
heated is not changed into earth but that a part of the 
matter of which the glass is composed is dissolved by the 
water. The analytical work of Scheele afterwards showed 
that this residue had the same components as the glass, 
thus confirming the work of Lavoisier. The old notion 
of transmutation was thus proved to be false and the 
important generalization was established that matter 
can neither be destroyed nor created. This principle 
of the conservation of mass is one of the fundamental 
laws of science. Of course, Lavoisier^s work was only 
the beginning of the series of experiments on this sub- 
ject which after many years established the law. 

The Atmosphere. — Priestley performed various ex- 
periments upon the gases known to him with the aid 



50 HISTORY OF CHEMISTRY 

of the pneumatic trough which he practically invented. 
He discovered the relation of plants and animals to the 
atmosphere and the approximate balance maintained 
by their action upon it. His inaccinrate analytical work 
and his devotion to the phlogiston theory prevented 
his reaching a true explanation of the facts observed 
by him. Scheele determined the composition of the at- 
mosphere, and later Cavendish made an exact analysis 
of it. Lavoisier had shown that it consisted of oxygen 
and nitrogen and had determined the proportions of 
each. He was, therefore, in a position to complete and 
explain the work of Priestley. The processes of breathing 
and of calcination were chemically analogous. Oxygen 
was drawn into the lungs by the respiration of animals, 
and there he thought it combined with carbon and the 
carbonic acid, or the ^^ fixed air'' of Black, was breathed 
out. This was noxious to other animals and this it was 
which was removed by plants. 

The Nature of Heat and of Matter. — Lavoisier dis- 
proved the old ideas as to the elemental nature of heat; 
yet apparently he believed it to have material existence. 
He wrote of a matiere de chaleur which he also called 
calorique. He ascribed to it a fluid (gaseous) nature 
but said it had no weight. His idea and also his views 
upon the constitution of matter are perhaps best given 
by a citation from his Reflexions sur le Phlogistique, 
Matter, he says, consists of small particles which do not 
touch one another, otherwise the diminution in volume 
on cooling could not be explained; between these par- 
ticles is the calorique. In gases there is most of this calo- 
rique; in solids least. In his experiments with Laplace 
upon specific heat he showed that solids differ in their 



THE FOUNDATIONS 51 

capacity for taking up this heat. His views are in par- 
tial accord with the modern theory of heat when he comes 
to define that form of energy. He says, ''Heat is the 
result of invisible motion of the particles, the sum of 
the product of the masses multiphed by the square of 
the velocities.'' 

Investigation of Organic Substances. — Lavoisier 
also occupied himself with organic chemistry, or the 
chemistry of life products, and made a beginning towards 
a scientific study of it in devising a method of analysis 
by which these substances could be burned and the water 
and carbon dioxide formed could be measured. Of 
course such a method was impossible until the compo- 
sition of these two substances themselves was definitely 
fixed. That these substances, as well as carbon in imper- 
fect combustions, were formed on burning organic sub- 
stances had long been known. Their nature, however, 
and the question as to their pre-existence in the or- 
ganic substances had been the subject of much discussion. 
Through his analysis Lavoisier determined that all 
organic substances were composed of carbon and hydro- 
gen, sometimes oxygen, and less often nitrogen and 
other elements. 

Theory as to Acids. — Thus much false theory and 
confusion in the science had been removed and the founda- 
tions for a new system had been laid. Simple bodies or 
elements were recognized; these formed compounds by 
the union of their particles drawn together by an attrac- 
tive force, affinity, and heat had its part to play in these 
masses. The multiplicity of compounds made necessary 
a system in their arrangement — such a system as would 
bring out and explain their interrelations. The funda- 



52 HISTORY OF CHEMISTRY 

mental reaction was oxidation. Lavoisier recognized 
the parts played by oxygen in the formation of acids, 
of oxides, and of salts. For these he gave the simple 
definitions which form the foundations of the new chem- 
istry. 

1. An acid results from the union of a simple body, 
ordinarily non-metallic, with oxygen. 

2. An oxide is a compound of a metal and oxygen. 

3. A salt is a compound of a metal and oxygen. 
This system was extended further for the sulphides, 

phosphides, etc., but the true nature of the chlorides was 
not known and the hydracids were discovered some years 
later. With their discovery the part played by hydrogen 
became clearer, but a century had to pass before this 
could be even approximately explained. 

The overthrow of the followers of Stahl and the accept- 
ance of Lavoisier^s ideas ushered in a new era in chem- 
istry. A new nomenclature was called for and it was 
created by Lavoisier and the French Encyclopedists. 
Of course, as knowledge grew mistakes had to be cor- 
rected and changes made, but the essential founda^tions 
had been laid. 

Elements. — It will be helpful here to trace the growth 
in the ideas regarding the elements, as the proper defi- 
nition of these was one of the most important and far- 
reaching changes introduced by the new system. Al- 
chemists and chemists seemingly had not attached 
much importance to this matter up to this time and the 
distinctions drawn were rather hazy. Hitherto the 
name had covered mainly philosophical speculations; 
henceforward they were to form the basis of systematic 
chemistry. The four-element theory of Empedokles 



THE FOUNDATIONS 53 

and Aristotle was a dream, a philosophical figment with- 
out basis or confirmation in real experiments. These 
elements were regarded as principles with certain mate- 
rial characteristics, entering, all or some of them, into 
every known substance and not necessarily capable of 
independent existence themselves. Some chemists, in- 
deed, undertook to prove that certain substances did 
contain these principles. There was no attempt, how- 
ever, at a general proof. 

The first clarifying definition was given by Boyle 
(1661), who was far ahead of his times. He defined ele- 
ments as ^^ certain primitive and simple bodies which, 
not being made up of any other bodies, or of one another, 
are the ingredients of which all those called perfectly 
mixed bodies are immediately compounded, and into 
which they are ultimately resolved.'' He did not be- 
lieve himself warranted by the knowledge then pos- 
sessed in proclaiming the positive existence of such 
elements. 

During the phlogistic period less and less importance 
was attached to the old ideas as to elements, and the 
belief gradually sprang up that a true element must be 
something which could be prepared and was not sub- 
ject to change. Macquer, in his Dictionary of Chem- 
istry , defined elements as ^^ those bodies which are so 
simple that they can not by any known method be decom- 
posed or even altered and which also enter as princi- 
pal or constituent parts into the composition of other 
bodies which are therefore called compound bodies.'' 
But he adds, ^^The bodies in which this simplicity has 
been observed are fire, air, water, and the purest earths." 
Black proved that certain chemical substances were 



54 HISTORY OF CHEMISTRY 

possessed of a constant and definite composition and 
fixed properties, unalterable, and hence simple bodies 
or elements. Lastly, Lavoisier in this Traite de Chimie 
enunciated his definition of an element as follows: ^'An 
element is a substance from which no simpler body has 
as yet been obtained; a body in which no change causes 
a diminution of weight/' Nearer to the modern theory 
he could not come without knowledge of the atoms and 
of allotropism. Under such conditions a number of 
substances were classed as elements which did not belong 
to the list. Lavoisier first classed the metals as elements. 
Spread of the New Chemistry. — The teachings of 
Lavoisier or, as Fourcroy styled it, the ^^ French Chem- 
istry," speedily found acceptance in France, in England, 
and (through the influence of Klaproth) in Germany, 
where at first the opposition had been intense. By the 
close of the century chemists almost universally had 
given in their adherence to the new doctrines. Chem- 
istry now had the basis of a true theory and, what was 
of greater value, the knowledge that theories could be 
deduced only from the weight relations of actually occur- 
ring reactions. There were to be no baseless and delu- 
sive dreams for the future, although mistakes might 
be made in the interpretation of facts. We find that 
though facts rapidly increased in number theories were 
slowly evolved and gained acceptance only after most 
careful weighing and testing in every known way. In 
this respect the experience of the past was invaluable. 
Great names, so-called authorities, might gain a hear- 
ing for a theory but had to show that it was the best 
logical explanation of facts and laws. Men had cast 
off forever the burden of authority in science. 



THE P0UNDATI0N8 55 

Black (1728-1799). — There should be mentioned 
at this time three distinguished chemists, who were 
of great service in making important discoveries and 
improving methods and made noteworthy contributions 
to the progress of chemistry. The first of these, Joseph 
Black, was of Scotch parentage and, while a student 
at the University of Glasgow, undertook an investi- 
gation into the cause of the causticity of magnesia, lime, 
and the alkahs. Caustic lime, or quick lime, was made, 
for instance, by the burning of limestone. Its caustic- 
ity was supposed to be conferred upon it by the heat 
of the fire, and this could be transferred by the proper 
treatment of a mild alkali with quick lime to the caustic 
alkali. Using magnesia alba in his experiments, he found 
that there was a loss of weight on heating it and the 
substance magnesia usta was formed. On treating mag- 
nesia alba (magnesiima carbonate) with oil of vitriol 
there was effervescence from an escaping gas, and epsom 
salt or magnesium sulphate was formed. This was also 
formed from magnesia usta (magnesium oxide) and oil of 
vitriol but there was no escaping gas. Mild alkali effer- 
vesces on the addition of oil of vitriol but caustic alkali 
does not. The reasoning then was plain. The pres- 
ence of the gas set free from magnesia alba and not 
from magnesia usta makes the difference between the 
two, and it is also the gas present in mild alkali which 
enables it to change magnesia usta into magnesia alba, 
leaving caustic alkali. The burning of magnesia alba 
or of limestone consists then in the driving off of this 
gas which Black called ^^ fixed air. ^' This fixed air was 
afterwards studied by Priestley, who invented the in- 
valuable pneumatic trough to aid him in his researches. 



S6 HISTORY OF CHEMISTRY 

Priestley identified this with the gas issuing from fer- 
mentations in breweries. Thus carbon dioxide became 
known. Priestley later discovered carbon monoxide. 
Black devoted much time to experiments upon heat and 
made the brilliant discovery of latent heat, or the heat 
concerned in changes of physical state. 

Priestley (1733-1804). — The second of these chem- 
ists was Priestley who was born near Leeds in England 
and was largely seK trained, as he had the advantage 
of a high school training only. On account of pohti- 
cal and religious persecution he left England, and the 
later years of his hfe were spent in America, near Phila- 
delphia. Priestley was a brilliant investigator, per- 
forming many most striking experiments. He was not 
thorough, however, nor very accurate, possessing little 
analytical skill, and was lacking in the scientific acumen 
needed for the proper interpretation of his results. It 
was upon the gases that his most valuable work was 
done, his pneiunatic trough enabling him not only to 
discover new gases but to investigate the properties 
of a number of those already partially known. 

Discovery of Oxygen. — His method of experimen- 
tation is well illustrated by his account of his discovery 
of oxygen. ^'Having procured a lens I proceeded with 
great alacrity to examine by the help of it what kind 
of air a great variety of substances would yield, put- 
ting them into vessels filled with quicksilver and kept 
inverted in a basin of the same. After a variety of other 
experiments I endeavored to extract air from mercurius 
calcinatus per se (red oxide of mercury) and I presently 
found that by means of this lens air was expelled from 
it very readily. Having got about three or four times 



THE FOUNDATIONS 57 

as much as the bulk of my materials I admitted water 
to it and found that it was not imbibed by it. But what 
surprised me more than I can well express was that a 
candle burned in this air with a remarkably vigorous 
flame. I was utterly at a loss to account for it.^^ His 
experiments showed him that this air ^^had all the prop- 
erties of common air, only in much greater perfec- 
tion/^ and he called it ^^dephlogisticated air/' regarding 
it as very pure ordinary air. 

Study of the Atmosphere. — Priestley seems to have 
looked upon all gases as easily changeable one into the 
other, at least in the first part of his work. He made 
many experiments as to the action of the various gases 
known to him upon animals and plants. He would place 
a mouse in a jar of the gas and notice the effect upon its 
breathing and general life processes. Plants were grown 
in similar jars and the result upon the growth noted. 
He showed that air, which had become noxious through 
breathing or the burning of a candle, could be restored to 
its original condition by growing a plant in it. This, he 
said, was due to the impregnation with phlogiston in the 
first case and to its removal in the second. ^^It is very 
probable," he wrote, ^Hhat the injury which is continu- 
ally done to the atmosphere by the respiration of such 
a number of animals as breathe it and the putrefaction 
of such vast masses both of vegetable and animal sub- 
stances exposed to it is, in part at least, repaired by 
the vegetable creation." He was unable to explain 
how this was done as he was a poor analyst. This lack 
of analytical skill is shown in his experiments on the 
formation of water by exploding mixtures of hydrogen 
and oxygen (plus air) in a copper globe. He obtained 



58 HISTORY OF CHEMISTRY 

a blue liquid whose nature he was unable to determine. 
The analyst whose aid he soUcited showed him that it 
was a solution of copper nitrate in water. The fact that 
nitric acid was thus formed induced him to deny that 
water was a compound of oxygen and hydrogen. In 
the hands of Cavendish, a more thorough and careful 
investigator, this discovery led to the demonstration of 
the composition of nitric acid. 

Views as to Combustion. — He held that all combus- 
tible substances contained hydrogen. This was, in his 
view, phlogiston. The metals contained it and their 
calces, or oxides, were simply the metals deprived of 
hydrogen. Thus he showed that when iron oxide was 
heated in hydrogen gas the hydrogen was absorbed and 
metalUc iron formed. Rich iron slag was, in his opin- 
ion, iron with some hydrogen retained. To prove this, 
it was mixed with the carbonates of the alkahne earths 
and heated strongly. This gave him an inflammable gas 
and, according to his beUef, all inflammable gases were 
hydrogen in a more or less impure condition. It was 
later that he discovered carbon monoxide — also nitrogen 
dioxide — and he found that water could be impregnated 
with carbon dioxide and suggested its use in disease. 



CHAPTER VIII 

THE ATOMIC THEORY 

The Proposition of Lavoisier. — The ground work of 
the new system of chemistry was laid by Lavoisier in 
the following propositions: 

1. In all chemical reactions, only the form of the 
materials changes, the quantity remaining the same. 
The substances used and the products obtained can be 
brought into an algebraic equation by means of which 
any one unknown member may be calculated. 

2. In all combustions the burning body unites with 
oxygen, and in general an acid is formed by combustion 
of a non-metal, and a metallic calx is formed by com- 
bustion of a metal. This calx is an oxide. 

3. All acids contain oxygen united with a base or a 
radical which, in the case of inorganic substances, is 
generally an element; in organic substances it is made 
up of carbon and hydrogen, and often contains nitrogen 
and phosphorus as well as other elements. 

The next stage in this inquiry into compounds and 
combination concerned the method or process of com- 
bining. What were the combining particles? Here re- 
course to the Greek philosophers was once more necessary, 
but sure and enduring foundations had to be laid in sup- 
port of the old-world vision which had been practically 
lost sight of. A new Atomic Theory became a necessity. 
For this we are indebted to John Dalton. 

59 



60 HISTORY OF CHEMISTRY 

Richter (1762-1807) — It is well, however, to refer 
first to the work of Richter who, through careful ana- 
l3rtical work, constructed a table giving the proportions 
by weight in which substances combine. This was a 
distinct advance on the afl&nity tables which have been 
mentioned. Richter had noted with keen interest that 
one neutral salt could react with another, and that by 
interchange two other neutral salts could be formed 
without change of reaction towards test-papers. The 
neutrality was preserved, showing an equivalence be- 
tween the amounts entering into combination. This 
was a most important observation, having its bearing 
on the law of definite proportions, and the table of equiva- 
lents may be regarded as the forerunner of the atomic 
weight table. 

Dalton's Atomic Theory. — John Dalton (1766-1844) 
was more of a mathematician and physicist than a chemist. 
Most of his life was spent in Manchester, England, as 
instructor in mathematics and natural philosophy, which 
then included some chemistry. He was very poor, be- 
ginning to support himself by teaching at twelve years 
of age, and was largely self taught. He was forced to 
make most of his own apparatus and lacked skill in 
carrying out experiments, and in chemical manipulation 
fell far behind Priestley. But he excelled in logical 
deductions and in generahzations from his facts, his 
aim being the establishment of general, underlying laws. 
Priestley was a briUiant discoverer; Dalton a clear, 
logical, mathematically trained thinker. 

Constitution of Mixed Gases. — For years he had been 
interested in meteorological observations. Those which 
he made upon dew and aqueous vapor existing in the 



THE ATOMIC THEORY 61 

air led him to the pubhcation in 1801 of an important 
paper upon the Constitution of Mixed Gases, This 
was followed by other papers on the properties of gases 
and these prove that he had formed the idea that gases 
were made up of small, distinct particles. He wrote of 
the pressure upon them and the repulsion between these 
particles and stated that ^'A vessel full of any elastic 
fluid (gas) presents to the imagination a picture like 
one full of small shot.'' He reported the discovery of 
some of the fundamental laws of gases. First, there was 
the law of expansion by heat, according to which all 
gases independent of their nature expand equally on 
heating. Another, the law of partial pressures, is still 
known as Dalton's Law. He found that the composition 
of the atmosphere is the same at low and high temper- 
atures and that heavy gases diffuse upward into hght 
and light downward into heavy, thus forming always 
a homogeneous mixture. He noticed that water did 
not dissolve all gases ahke but in amounts varying with 
their nature. As this matter of solution was a mechan- 
ical operation in his opinion, he reached the following 
conclusion: ^^I am persuaded that this circumstance 
depends upon the weight and number of the ultimate 
particles of the several gases, those whose particles are 
Hghtest and single being least absorbable and the others 
more. An inquiry into the relative weights of the ulti- 
mate particles is a subject, as far as I know, entirely new.'' 
He presented before the Manchester Literary and Phil- 
osophical Society in 1802 a paper which included ^^a 
table of the relative weights of the ultimate particles 
of gaseous and other bodies." 

To account for the diffusion of gases and so complete 



62 HISTORY OF CHEMISTRY 

his vision of the atmosphere, Dalton had to provide a 
repulsive force. This he solved ^'without letting in any 
other repulsive force than the well-known one of heat. 
. . . There was but one alternative left — namely, to 
surround every individual particle of water, of oxygen 
and of azote with heat and to make them respectively 
centres of repulsion, the same in a mixed state as in a 
simple state. . . . Atoms of one kind did not repel the 
atoms of another kind but only those of their own kind.'' 

Of course, the idea of the existence of atoms was neither 
new nor original with Dalton. The conception of the 
Greek philosophers was that: ^* The bodies which we 
see and handle, which we can set in motion or leave at 
rest, which we can break in pieces and destroy, are com- 
posed of smaller bodies which we cannot see or handle, 
which are always in motion and which can neither be 
stopped nor broken in pieces, nor in any way destroyed 
nor deprived of the least of their properties.'' 

Something of this conception was held and felt all 
through the earHer days of chemistry. The physicists 
Newton and Bernouilli held it (the latter believing the 
pressure exerted by a gas upon the enclosing walls to be 
due to the constant bombardment of the atoms), al- 
though merely the term particle was used by them and by 
Lavoisier, in whose mind the same idea was present. 
The credit which belongs to Dalton is that he took this 
dream and by means of collected facts and laws gave 
it that confirmation which was necessary in order that 
it might be ranked as a theory. While its conception 
was largely on physical reasoning, the grounding which 
brought general acceptance and established it as a funda- 
mental theory of science came when it served as the only 



THE ATOMIC THEORY 63 

satisfactory explanation of the fundamental laws of 
chemistry. This was also the contribution of Dalton. 

Law of Constant Proportions. — So far the theory 
as to the existence of atoms had a physical rather than 
a chemical basis. Its support came when it was recog- 
nized as the logical explanation of the basic laws of chem- 
istry. The first of these was the law of constant pro- 
portions, namely, that in any compound the relative 
proportions of the constituents are definitely fixed and 
will always be found the same. This, one might say, 
had been tacitly accepted by all analytical workers as 
the result of their experience and a necessary basis for 
their work. As the number of compoimds known in- 
creased and analytical methods improved in accuracy 
some doubt arose as to the fixity of these proportions. 
A discussion was carried on for several years between 
two distinguished French chemists, BerthoUet (1748- 
1822) and Proust (1755-1826), with regard to the ex- 
istence of any such regularity, and in the course of it much 
valuable analytical work was done and a number of new 
compounds discovered. This discussion aroused the 
interest of the leading chemists of the time. BerthoUet 
maintained that the proportions were variable and noted 
a number of apparent cases among oxides and other com- 
pounds. Proust showed that some of these oxides con- 
tained hydrogen, thus discovering the class of hydrox- 
ides, and in his analyses of the different oxides very nearly 
arrived at the law of multiple proportions. One of the 
good results of the controversy was to bring about a clear 
distinction between compounds and mixtures. Ber- 
thoUet lost most of his supporters before the close of the 
controversy. Another earnest supporter of the law of 



64 HISTORY OF CHEMISTRY 

definite proportions was Richter, though probably his 
work was unknown to Dalton. He pubUshed (1792-94) 
the results of his work upon the proportions by weight 
in various compounds under the title of ^^A Foundation 
for the Stoichiometry or Art of Measuring Chemical 
Elements/' This is the first work on systematic quan- 
titative analysis. It was a decade or more before Rich- 
ter's excellent work received appropriate recognition. 
Law of Multiple Proportions. — It has already been 
pointed out how the fact that when two elements com- 
bine to form a compound the proportion of each is abso- 
lutely fixed and constant became firmly incorporated 
in the science and a recognized, even if unstated, law. 
This to the seeing eye meant a combining of atom with 
atom, though sometimes it might mean a greater number 
of atoms, provided this number was always the same. 
There is another law where the call for discrete par- 
ticles of fixed weight is still clearer. With these two funda- 
mental laws there was an assured basis for Dalton's 
theory of the existence of unchanging atoms. This 
second law is known as the law of multiple proportions 
and was discovered and announced by Dalton himself. 
The careful analytical work of Proust and Berthollet 
and others gave him the necessary facts for his general- 
ization. Considering these facts, he found that when 
two elements combined to form one compound there were 
certain definite proportions in which they united. If 
they formed more than one compound, under changed 
conditions, then the proportion of one progressed by 
regular increments, an increase of once or twice the first 
proportion or some simple multiple of it. For this he saw 
that his hypothesis of atoms gave a plausible explanation 



THE ATOMIC THEORY 65 

— and the only plausible one — the increase correspond- 
ing with a doubUng, trebling, etc., of the weight of the 
original atoln. It was this that immediately attracted 
the attention of the leading chemists. Many set out to 
test the truth of the law and with its establishment 
the case was won. 

Dalton told his theory to Thomson, a noted chem- 
ist who was the author of some of the leading text-books 
of his day. Thomson pubhshed Dalton's views in his 
System of Chemistry in 1807. Sir Humphry Davy 
opposed the new hypothesis, but was won over to it and 
so were WoUaston and others, though they saw difficul- 
ties in its application which greatly delayed its general 
acceptance. The essential parts of Dalton's theory can 
be put in two sentences: 

1. Every element is made up of similar atoms of con- 
stant weight. 

2. Chemical compounds are formed by the union of 
the atoms of the different elements in simple numerical 
relations. 

All analytical work has been based on these two as- 
sumptions and the results have confirmed them. Dalton 
further speculated on the nature of the atoms, regard- 
ing them as spheres surrounded by an atmosphere of 
heat, not touching one another but in constant motion. 

Determining the Weights of the Atoms. — If the 
atomic theory were a true explanation of the facts of 
chemical combination, then its first and most important 
application would lie in a determination of the relative 
weights of the atoms of the various elements. This 
might be arrived at by a determination of the combin- 
ing proportions entering into different compounds, 



66 HISTORY OF CHEMISTRY 

provided the number of atoms in such compounds were 
known. Now it was in this that the supporters of the 
theory met their first and greatest diflSculty. By what 
possible means could the nimiber of the constituent 
atoms in a compound be accurately known? 

Dalton's Rules. — Following up his conception of 
the existence of atoms Dalton began to determine their 
relative weights, taking for his standard or unit hydro- 
gen, the lightest of them. A list of these weights as deter- 
mined by him was published in 1805. They show very 
faulty work and were superseded later by the remark- 
ably accurate results obtained by Berzelius. These 
weights as given by Dalton seem to have come very 
sHghtly into use. To overcome the difficulty of telling 
how many atoms entered into combination to form a 
particle of any compound, he adopted some very arbi- 
trary rules which were afterwards shown to be without just 
basis. These rules had the merit of simplicity, how- 
ever, and were about the best that could be formulated 
at that time. First, he divided compounds into binary, 
ternary, quaternary, etc., according as they contained 
two, three, four, or more atoms. Then he adopted the 
following rules : 

1. When only one combination of two bodies can be 
obtained it must be presumed to be a binary one unless 
some cause appear to the contrary. 

2. When tWo combinations are observed they must 
be presumed to be a binary and a tertiary. 

3. When three combinations are obtained we may 
expect one to be a binary and the other two tertiary. 

4. When four combinations are observed we should 
expect one binary, two ternary, and one quaternary, etc. 



THE ATOMIC THEORY 67 

How simple the whole matter would be if nature always 
chose the simplest, plainest paths! But happily for our 
development, she often has a confusing way of leading 
into many by-paths. Besides this difl&culty as to the 
number of atoms, Dalton's use of the term atom was 
often misleading. He made little distinction between 
the ultimate particles of elements or of compounds or 
the ideal indivisible atom. This was a most serious 
flaw. It caused Dalton himself to reject the work of 
Gay-Lussac; and it caused others, seeing these incon- 
sistencies, to hesitate to accept Dalton's views. Two 
things were much needed — a clearer definition of atoms 
and some reUable method of determining the number of 
atoms in a compound particle. 

Gay-Lussac (1778-1850). — The latter problem was 
partially solved by the labors of Gay-Lussac. This dis- 
tinguished pupil of BerthoUet was a well-trained chem- 
ist, capable of very accurate analytical work and pos- 
sessing scientific acumen in a very high degree. He 
enriched chemical hterature by many excellent investi- 
gations, working often in company with Thenard, Hum- 
bolt, and Liebig. His most noteworthy work was upon 
iodine, cyanogen (the first compound radical), the alka- 
hne oxideSj the isolation of boron, improved methods 
for organic analysis, and many similar studies. 

Law of Volumes. — His name is especially associated 
with his researches upon the combining volumes of gases. 
He discovered the law of the expansion of gases under 
the influence of equal temperature increments. He also 
studied the combining volumes of gases and deduced 
from his experiments the law of volumes for gases. This 
law of volumes may be stated thus : The volumes in which 



68 HISTORY OF CHEMISTRY 

two gases combine bear a simple ratio to one another 
and to the volume of the resulting gaseous product. Thus 
one volume of oxygen always reacts with two volumes 
of hydrogen to form two volumes of steam. Any excess 
of either oxygen or hydrogen will be left over. So also, 
one volume of nitrogen unites with exactly three vol- 
umes of hydrogen and two volumes of ammonia result. 
The accoimt of his work and the conclusions he drew 
from it were given in 1808. 

Objections to the Law. — Gay-Lussac was well ac- 
quainted with Dalton's hypothesis and showed in part 
how his discoveries accorded with it. A similar molecu- 
lar condition was essential in order that all gases should 
behave ahke towards pressure and changes of tempera- 
ture, and, in addition, obey his law of volumes. In other 
words, equal volumes of gases must contain equal num- 
bers of molecules. Gay-Lussac made no distinction be- 
tween these molecules and atoms, recognizing but one 
kind of final particle. Dalton took exception to this 
reasoning, and in his reply said that he too had once 
held the same idea as to combining volumes but had 
seen that it was untenable. He further maintained that 
the experiments of Gay-Lussac were inaccurate and that 
the gases did not combine exactly by volumes but often 
by fractions of volimaes. His argument may be illustrated 
best by taking some substance, as hydrochloric acid, 
as an example. One atom of hydrogen chloride consists 
of one atom of chlorine and one atom of hydrogen. On 
combination of equal volumes of these two gases, there- 
fore, there should result but one volume of hydrogen 
chloride if the supposition that equal volumes of gases 
contain equal numbers of final particles is correct. On 



THE ATOMIC THEORY 69 

the contrary, the yield is two volumes of hydrogen chlo- 
ride. If these final particles were atoms, then the result- 
ing volumes of hydrogen chloride must each contain 
only half as many particles as the volumes of the com- 
bining gases or the hydrogen chloride is made up of half- 
atoms of hydrogen and chlorine. This reasoning is 
manifestly final so far as the theory of the volumes con- 
taining the same number of atoms is concerned unless 
some different definition of atoms is assumed. 

Avogadro's Theory. — The solution of the difl&culty 
was shown by Avogadro (1776-1856) in 1811. This 
Itahan physicist made a distinction between two 
kinds of ultimate particles which we know as molecules 
and atoms. The molecules were compound particles 
and were made up of the indivisible atoms. In hydrogen 
gas, therefore, we have as the final particles molecules, 
each made up of two atoms of hydrogen; and a molecule 
of oxygen is made up of two atoms of oxygen and chlo" 
rine has two atoms to the molecule. With this hy- 
pothesis the volume relations, as given by Gay-Lussac, 
become entirely regular and intelhgible. These dis- 
coveries of Avogadro have been sometimes credited to 
the French physicist Ampere, but his statement appeared 
three years later (1814) and lacks the clarity and full- 
ness of that of Avogadro. He assumed the presence of 
four atoms instead of two in the molecules of elementary 
gases and attempted to extend his hypothesis to the 
constitution of molecules existing in solids. His mem- 
oir first appeared in the form of a letter to BerthoUet 
and he showed in it his ignorance of the work of Avo- 
gadro. 



CHAPTER IX 

THE ATOMIC WEIGHTS 

Taking hydrogen as the unit, Dalton determined a 
small nvmiber of atomic weights but, lacking skill as a 
chemist, his results were so faulty as to cause much un- 
certainty with regard to the whole matter. Other chem- 
ists took up this task with greater success. Chief among 
these was Berzelius, who in conjunction with his pupils 
undertook the determination of the atomic weights of 
all the known elements. The analytical work, of course, 
greatly excelled that of Dalton and in the rules laid 
down for his guidance in deciding the number of atoms 
in a given compound or molecule his intimate knowl- 
edge of the chemical behavior of many substances, his 
acuteness of observation, his attention to the smallest 
details, and his painstaking patience render his work 
truly remarkable. Many of his atomic weights are 
still quoted and made use of in settling these physical 
constants over which chemists have been busied for 
so long a time. His standard was oxygen taken as 100. 
Still he was at a loss for a rehable method of telling how 
many atoms there were in the molecules with which he 
dealt, and his rules for settling this question were in 
some respects arbitrary and unsatisfactory. As knowl- 
edge grew and new aids were discovered for arriving 
at the number of atoms in a molecule, he availed him- 
seK of them and corrected his tables of the atomic weights 

70 



THE ATOMIC WEIGHTS 71 

which he issued every now and then through a number 
of years. 

The Standard for the Atomic Weights. — Since the 
atomic weights are necessarily relative to that of some 
one elementary atom taken as the unit or standard, 
it is essential that the standard shall be the best avail- 
able and universally recognized as such. The standard 
has been changed several times since Dalton chose hy- 
drogen, the Hghtest known atom, and assigned to it the 
unit value. Hydrogen, however, forms comparatively 
few compounds with the other elements and that means 
that in most cases the relative value could be determined 
only indirectly. A httle later Wollaston chose oxygen, 
giving it the value one. This had the disadvantage of 
giving fractional values for several of the atomic weights. 
It was probably to avoid this that Berzelius, when he 
chose oxygen for his standard, assigned it the value 100. 
Oxygen was chosen because of the large number of com- 
pounds which it formed and hence the possibility of 
direct determinations. Under this system some of the 
atomic weights were inconveniently large, running over 
one thousand. Some years later hydrogen was restored 
(largely through the influence of Gmelin) to its position 
as standard with the value 1 and held this position until 
near the close of the nineteenth century. In the early 
part of the last decade of that century the prolonged 
discussion came 'to an end by the general adoption of 
oxygen as the standard with the value 16 and the ap- 
pointment of an international committee which was 
to have charge over all corrections in the atomic weights 
and issue annually tables containing all revisions accepted 
by them. 



72 HISTORY OF CHEMISTRY 

Wollaston's Equivalents. — The uncertainty connected 
with the atomic weights as determined under Dalton's 
rules, or indeed under any arbitrary method of proce- 
dure, led WoUaston, his fellow countryman, to suggest 
abandoning the use of the term atom and substituting 
that of equivalent. This term he adopted from the work 
of Richter. WoUaston meant by it the relative quanti- 
ties or proportions in which bodies unite, thus doing 
away with the idea of atoms. He hoped in this way to 
escape all question as to the number of atoms in a com- 
pound. It is easy to see that his method rather increased 
than diminished the complications, and the atomic theory, 
which was based on fundamental laws, was to be done 
away with because of difficulties in settling their weight. 
Still the desire to eliminate theory was strong and many 
chemists, especially the English, continued to use the 
term equivalent for many decades after the time of 
WoUaston. The difficulties wiU be seen if examples are 
taken. Using WoUaston's standard of oxygen equal 
to 1, we find there are two compounds with carbon. 
One gives the ratio of carbon to oxygen as 0.75 to 1; 
the second gives the ratio of 0.375 to 1. Which ratio 
shall be taken? If the least equivalent is taken, then 
what is the other? Manifestly the knowledge of the 
number of the particles in the compound is just as essen- 
tial for equivalents as for atoms. 

Law of Specific Heats. — In the year 1819 Dulong 
and Petit, while experimenting upon the specific heats 
of the metals and other substances, came upon the im- 
portant truth that these were very nearly inversely 
proportional to their atomic weights. Multiplied by their 
atomic weights they gave a constant quantity which is 



THE ATOMIC WEIGHTS 73 

called the atomic heat. The law as stated by the authors 
is: The atoms of the different elements have the same 
capacity for heat. It is possible, therefore, by means 
of the specific heat to approximate the true atomic weight 
and arrive at a decision as to which of two or more 
possible figures represent the correct weight. 

There were exceptions to the law which were explained 
later. Still the law was extended to simple chemical 
compounds and proved of use after it was more fully 
understood. Berzelius opposed the acceptance of it at 
first, partly because it would necessitate a revision of 
his table of atomic weights and might endanger accepted 
views as to the atomic relations. He gradually gave up 
this stand when the law was confirmed by other workers 
and determinations more accurate than the first ones 
of Dulong and Petit were made of the specific heats. 

Isomorphism. — In the same year Mitscherlich an- 
nounced what was called the law of isomorphism. While 
engaged in a research upon the salts of phosphoric and 
arsenic acids, he reached the conclusion that compounds 
of analogous composition and containing the same number 
of atoms crystallize in the same form or, in other words, 
are isomorphous. For this to be really useful in deter- 
mining atomic weights it was necessary to reverse it and 
to have it hold true that isomorphous compounds were 
analogous and contained the same number of atoms. 
Here many difficulties presented themselves, necessi- 
tating narrower and narrower definitions of isomorphism. 
It is evident that though analogy or similarity of crys- 
tal form may have a bearing upon the molecular composi- 
tion and arrangement, we are as yet unable to determine 
fully this bearing. Berzelius took up the discovery of 



74 HISTORY OF CHEMISTRY 

Mitscherlich with enthusiasm and made frequent use 
of it in testing his atomic weights. 

Electro-chemical Equivalents. — Mention should be 
made in this connection of Faraday's law. This was 
deduced from his experiments in 1834 on the dissociat- 
ing action of the electric ciu*rent upon electrolji^es. In 
decomposing different electrolytes such as water, metalUc 
chlorides, etc., he found that there separated at the 
positive or negative electrodes equivalent amounts of 
respective constituents, provided the same quantity of 
electricity were used. The amounts separated were called 
the electro-chemical equivalents. The intensity of the 
ciu*rent needed to bring about the decomposition he re- 
garded as a measure of the force of affinity. Faraday 
thought that the determination of these equivalents 
would prove a valuable aid to the correct determina- 
tion of the atomic weights. The application of this 
method is to a certain extent hmited but it has been 
used in some recent accm*ate determinations. 

Work of Dumas on the Atomic Weights. — In their 
work upon the atomic weights Dumas and other French 
chemists made especial use of the law of volumes as 
given by Gay-Lussac and adopted the distinction made 
by Avogadro between atoms and molecules. The equiva- 
lents suggested by WoUaston were rejected by them as 
applicable only to a limited range of substances, such as 
acids and bases, besides being indefinite or not deter- 
minable when identified with combining weights, since 
many substances united in several different proportions 
to form compounds. Some of Dumas' determinations, 
as those of phosphorus, tin, and silicon, show that he 
did not reaUze the full importance of Avogadro's theory 



THE ATOMIC WEIGHTS 75 

as an aid in such determinations. Still he beUeved that 
this theory gave a surer basis for solving such questions, 
and drew up a table of atomic weights making use of 
it and the law of Dulong and Petit. He used the term 
elementary molecules and said that there was no means 
of deciding how many smallest particles these mole- 
cules contained. In acdKacy and correctness his work 
fell below that of Berzehus. 

Vapor Densities. — Dumas devised an accurate and 
excellent method for determining the specific gravities, 
or densities, of gases which could be used at high temper- 
atures, thus enabling him to experiment upon the vapor 
densities of iodine, phosphorus, sulphur, mercury, etc. 
His results, instead of confirming, tended rather to dis- 
prove the law of volumes. The trouble lay in the com- 
plex nature of the molecules experimented upon, but of 
course this was unknown to Dimias. He finally de- 
clared that even in the case of the simple gases hke vol- 
umes did not contain equal numbers of chemical atoms. 
Berzehus also had been practically forced to give up 
the law of volumes, at least so far as any use in atomic 
weight determinations was concerned, hmiting its appli- 
catidn to the uncondensed or so-called permanent gases. 

Chemists therefore looked with indifference or dis- 
favor on this law which is the mainstay of modern work 
upon the atomic weights. The law of Dulong and Petit 
was also shown to have some notable and unexplained 
exceptions, and Mitscherlich by his further discovery 
of dimorphism had thrown much doubt upon his law of 
isomorphism. So at the close of the thirtieth year of the 
nineteenth century the atomic theory was regarded by 
many chemists as relegated to a hypothetical position. 



76 HISTORY OF CHEMISTRY 

GmeUn's Views. — Some took up again the equivalents 
of Wollaston. Certainly little distinction was made be- 
tween these and the atoms of Dalton, and the duahstic 
system of Berzehus lost ground. GmeHn, the author 
of the most complete handbook or encyclopedia of chem- 
istry up to his time, and the most influential as it went 
through many editions and formed the basis subsequently 
of Watts' Dictionary of Chemistry , was the leader in this 
new school of chemistry. In the edition of his handbook 
published at this time, the fourth decade, he gave up the 
atomic theory altogether. He recognized no difference 
between chemical compounds and mixtm^es. Two sub- 
stances, according to his ideas, could combine in an un- 
ending number of proportions. In the case of a strong 
affinity between them the tendency was toward a limita- 
tion to a few proportions. To each substance then a 
sort of mixing weight could be assigned and this number 
could be used in analytical calculations. His table of 
equivalents halved most of the atomic weights. Thus, 
H = 1, O = 8, S = 16, C = 6, etc. Water became HO. 
The rule was to make everything conform to the utmost 
simplicity. Where there was choice between several 
possible equivalents for any one element he took the 
the least and simplest. These nimibers and formulas 
were retained by many chemists for some decades after- 
wards. 

Confusion in the Sixth Decade. — The middle of the 
centm-y saw the condition of affairs regarding these 
physical constants a badly mixed one. Two units or 
standards were in use. Dalton had used hydrogen as 
the unit and this was adopted by Gmelin and many 
others. Wollaston and Berzehus took oxygen as the 



THE ATOMIC WEIGHTS 77 

standard, Wollaston giving it the value 10 and Ber-. 
zelius using the value 100, while Thomson gave it the 
value 1. But, far worse than having two standards, 
widely differing values were assigned for the atomic 
weights and all needed revision. In Germany, for in- 
stance, the value for carbon was 6 and for oxygen 8. 
In France these values were respectively 3 and 8. 

Revisions of the Atomic Weights. — Dimias was es- 
pecially active in the revision of these numbers. His 
determination of the atomic weight of carbon and his 
work, in conjunction with Boussingault, to determine 
the ratio of hydrogen to oxygen in water are classical. 
Dumas fixed the number 16 for oxygen. The exact re- 
sult was 15.96. This ratio has been the subject of more 
painstaking and careful determinations than any other 
in chemistry, yet without complete accord. Dumas 
also determined many other atomic weights. Others 
taking part in this work of revision were Erdmann, Mar- 
chand, Marignac, De Ville, and Scheerer, but easily 
the greatest of them all in care and acciu^acy was Stas. 
His work was monimiental in the pains taken to secure 
absolute accinracy, and yet in a few years errors were 
found and the so-called Dumas correction, as well as 
others, had to be applied to the numbers found by him. 
The atomic weights determined by him with the great- 
est care were those of silver, potassium, sodium, hth- 
ium, lead, chlorine, bromine, iodine, sulphur, and ni- 
trogen. 

Clearing up the Confusion. — The solving of the 
problems which confronted those devoting their atten- 
tion to the atomic weights and the clearing up of the 
existing confusion were in great measure brought about 



78 HISTORY OF CHEMISTRY 

through the development of organic chemistry. Much 
Ught was thrown upon the distinction between atoms 
and molecules and the dominant doctrine in this branch 
of chemistry quietly assiuned the truth of Dalton's theory 
in all its important particulars as the only satisfactory 
explanation of and adequate basis for the work done. 
Frankland's researches on the organo-metallic substances 
practically did away with the old confusion between 
atoms and molecules. Then, too, the value of Avo- 
gadro's law as an aid to the correct determinations of 
atomic weights became more fully recognized and lab- 
oratory methods were more accurate. This was notably 
the case in vapor densit}^ determinations. Much credit 
for placing atomic weight work upon a more satisfactory 
basis is due to Cannizzaro. In 1856 he published a small 
pamphlet in which he took a determined stand upon the 
necessity for the use of the means already at hand and 
especially the theory of Avogadro that equal volumes of 
gases contained equal numbers of particles. In 1860 a 
meeting was called at Karlsruhe by distinguished chem- 
ists of various nationalities to see if some general agree- 
ment could not be reached as to standards, atomic weights, 
and chemical notation. The meeting was presided over 
by Dumas. No general agreement was reached but 
Cannizzaro's pamphlet, in which he urged chemists to 
place reliance in the methods mentioned and so to cor- 
rect many of the false atomic weights then in use, was 
distributed towards the close of the meeting. His argu- 
ments proved convincing, resulting in the general adop- 
tion of the modern methods. 

Constancy of the Atomic Weights. — The question 
has repeatedly arisen as to whether the atomic weights 



THE ATOMIC WEIGHTS 79 

are variable within narrow limits. The approximate 
agreement of the best determinations would tend to 
exclude any other than a slight variation. This ques- 
tion Stas proposed for himself before starting upon his 
classic work on the atomic weights. The conclusion 
he drew from his experiments was that they were un- 
changeable. The question was raised again by Schlitz- 
enberger and Butlerow. These chemists supposed the 
range of variation to be very shght yet distinctly to be 
detected by analysis. Vogel also came to the conclusion 
that the atomic weights vary because those found by the 
use of certain compounds differ from those derived 
from other compounds. If this assumption is correct, 
then the law of conservation of mass and along with it that 
of constancy of proportions cease to fall under the cate- 
gory of laws. 

In 1906 Landolt put the law of conservation of mass 
to a critical test. A vessel was so arranged that two 
substances could be accurately weighed and then re- 
action allowed to take place between them without any 
possible loss of substance. A large number of experi- 
ments were carried out with every refinement as to ap- 
paratus. The second weighing revealed a difference of 
about one part in 10,000,000. Such differences do not 
exceed the unavoidable experimental error. 

A number of years ago Crookes suggested that one 
might assume the presence of a few of what he called 
'*worn atoms ^' in the countless numbers of others which 
must come under consideration in any atomic weight 
determination. Essentially, this means the presence of 
atoms of the same element which vary slightly in weight 
and mass. The presence of a few such atoms would es- 



80 HISTORY OF CHEMISTRY 

cape detection as falling within the experimental error. 
Within the past few years the theory of isotopes has 
grown up and it seems certain that such isotopes exist. 
In the case of gases they may be separated by the dif- 
fusion process. First, an isotopic neon atom was dis- 
covered, then hydrogen, chlorine, and others. These 
isotopes bear a very small ratio to the total nmnber of 
atoms present in any given volume. 



CHAPTER X 

NATURE OF THE ATOM 

It is worthy of note that from the very beginning the 
modern atomic theory laid httle or no stress upon the 
indivisibihty of the elementary atom. For all purposes 
of the chemist it was sufficient to know that under all 
manipulations and changes in the laboratory or in nature 
it seemed to remain intact and, therefore, could be as- 
sumed as an ultimate particle so far as experience went. 
Within a decade after the announcement of the theory 
there sprang up a hypothesis as to the possible com- 
poimd nature of the atom and hence its origin or gene- 
sis. This was the well-known Prout^s hypothesis which 
was announced in 1815. 

Prout's Hypothesis. — This hypothesis was based on 
the assumption that all the atomic weights were whole 
numbers and, therefore, multiples of the unit hydrogen. 
From this Prout reasoned that these elements were 
only different grades of condensation of hydrogen, which 
was, therefore, the primal element. No additional proofs 
were suggested in support of this theory. Prout, the 
author of it, was a physician and did little chemical 
work of value. Even if the atomic weights had been 
all whole numbers this was in itself no proof that they 
were made up of hydrogen. Yet this hypothesis proved 
to be an attractive one to many chemists. As the years 
passed the increasingly accurate determinations showed 

81 



82 HISTORY OF CHEMISTRY 

that some of the atomic weights were not whole numbers 
and that the fractions persisted, though improved work 
might vary them shghtly. 

Views of Berzelius. — Berzelius regarded the hypoth- 
esis with favor when first brought to his attention. 
He soon became its first and strongest antagonist. In 
1825 he pubhshed a table of the atomic weights which 
contained a number of fractions and he protested strongly 
against the practice of rounding off these fractions into 
whole numbers. As Hoffman says, '^He could not per- 
suade himself that the numerical relations of these val- 
ues betokened an inner connection of the elements nor 
yet a common origin. On the contrary, he was of the 
opinion that these apparent relations would disappear 
more and more as these values were more accurately 
determined. For him, therefore, there existed as many 
forms of matter as there were elements; in his eyes 
the molecules of the various elements had nothing in 
coramon with one another save their immutability and 
their eternal existence.^' Our later knowledge of these 
matters would tend to show that in this Berzehus had 
gone too far to the other extreme. 

Testing the Hypothesis. — In 1832 Turner was spe- 
cially delegated by the British Association to investi- 
gate this question. If barium, chlorine, etc., really had 
fractional atomic weights then the h3^pothesis in its 
original form was untenable. Turner's results were 
adverse to the hypothesis. So also were Penny's. Mar- 
ignac suggested that if half the atomic weight of hydro- 
gen were taken then all known atomic weights would 
be multiples of it. The idea was taken up by Dumas 
with enthusiasm but he found this factor must be once 



NATURE OF THE ATOM 83 

more halved, so one-fourth the hydrogen atom was 
taken. It is not quite clear why this was not a begging 
and abandonment of the whole question. But the very 
careful and accurate work of Stas upon the atomic weights 
made even this position impossible. And so the factor 
was by some shifted to one-tenth the unit and by Zan- 
gerle to the one-thousandth part of the hydrogen atom. 
With this it passed the hmit of experimental evidence 
and lost all weight and meaning. 

Numerical Relations between the Atomic Weights. — 
The first numerical regularities observed between the 
atomic weights were the triads of Dobereiner. This 
chemist seems to have observed first that the combin- 
ing weight of strontium was the arithmetical mean of 
those of calcium and barium. A Hke regularity was 
noted with regard to certain physical properties of these 
elements and some of their compounds. This led him 
for a while to question the independent existence of 
strontium. Several similar triads were discovered among 
the other elements as Hthium, sodium, and potassium; 
chlorine, bromine, and iodine; sulphur, selenium, and 
tellurium. He was careful not to let this grouping depend 
upon the atomic weights alone but insisted that only 
elements exhibiting decided analogies of properties 
should be considered together. This idea was taken 
up by other chemists, notably by Gmelin in his Hand- 
hook, and many analogies and groups were sought for. 
In 1857 Lennsen returned to this grouping, endeavor- 
ing to force all the elements into some twenty groups. 
Then Odling sought to build upon them an elaborate 
system of the elements which he called the Natural 
System. Such groupings were often forced and failures. 



84 HISTORY OF CHEMISTRY 

The science was not far enough advanced to enable one 
to understand the real meaning of these regularities. 

Gladstone's Ascending Series. — The first to suggest 
an arrangement of the elements in the order of their 
atomic weights, beginning with hydrogen, was Gladstone 
(1853). These numbers were too faulty and there was 
too much confusion in them to yield any satisfactory 
results, but the principle was an important one. Mani- 
festly nothing in the way of interrelation or regularity 
was to be found in tables alphabetically arranged. In 
1863 de Chancourtois made use of the revised atomic 
weights in an ascending series which he called the tel- 
luric screw. He drew as a conclusion from his work 
that the properties of an element are determined by 
atomic weight. This was a fundamental proposition in 
the Periodic System which was later announced by 
MendeleefE. In the work of Newlands, which followed 
closely upon that of de Chancourtois (the first publi- 
cation appearing in 1864), there is a nearer approach 
to the Periodic System. He also arranged the elements 
according to their atomic weights and observed that 
the eighth element was analogous to the first, and so on 
through the list with an interval of seven. This he 
called the law of octaves. There were many difficulties 
and inconsistencies so that little support was attracted 
to it. Meyer^s table, published in the same year, was 
arbitrary as to the sequence of the elements, arranged in 
sixes, and was too faulty to receive much attention. 

Periodic System. — It was Mendeleeff, a Ptussian 
chemist, who, independently and with a wealth of chem- 
ical facts adduced in its support, gave to the science its 
central system, bringing order out of much confusion. 



NATURE OF THE ATOM 85 

Because the elements fell in periods of sevens and threes 
it was named the Periodic System. The basic law was 
given in this form: ''The properties of the elements are 
functions of their atomic weights/^ So nearly is this 
true that Mendeleeff was able to predict the existence 
of certain elements, giving a number of their properties. 
These were later discovered and the prophecies con- 
firmed. It required an insight into the principles of 
this system to devise the later table given by Mendel- 
eeff, and the conclusions reached by him give evidence 
that he had grasped these principles. The most impor- 
tant of these were: 

1. The elements, if arranged according to their atomic 
weights, exhibit an evident periodicity of properties. 

2. Elements which are similar as regards their chem- 
ical properties have atomic weights which are either 
nearly of the same value or which increase regularly. 

3. The arrangement of the elements in the order of 
their atomic weights corresponds to their so-called val- 
ences as well as to some extent to their distinctive chem- 
ical properties. 

4. The elements which are most widely diffused have 
small atomic weights. 

5. The magnitude of the atomic weight determines 
the character of the element just as the magnitude of 
the molecule determines the character of a compound 
body. 

The table of Mendeleeff was changed but little for 
thirty years. Its anomahes, as the omission of hydro- 
gen and the rejection of the atomic weight as the decid- 
ing factor in such cases as cobalt and nickel, tellurium 
and iodine, etc., were recognized; but greater knowl- 



86 HISTORY OF CHEMISTRY 

edge was needed before these could be explained or the 
underlying law grasped. 

The Zero Group. — In discussing the Periodic System 
it had been pointed out by mathematicians that the 
transition yer saltum, as from fluorine to sodium or 
chlorine to potassiima (that is, an increase of electro- 
negative character until the maximum was reached in 
fluorine and then an abrupt change to the highly elec- 
tro-positive sodium), could not take place without first 
passing through either zero or infinity. When Ramsay 
announced, near the close of the nineteenth century, the 
discovery of argon, helium, and the other monatomic 
gases and it was found that these had no combining 
power, no electro-chemical character, and no valence 
and were the only known monatomic gases at ordinary 
temperature, it was seen that the zero group had been 
found and the table rounded off. The periods were no 
longer sevens but eights, besides the short periods of 
three. 

Contributions from Radioactivity. — The study of 
radioactive phenomena began in the first decade of the 
twentieth century. The radioactive elements, with every 
proof of their elemental character, increased by nearly 
fifty per cent the number of known elements. How 
could they find places in the system which was already 
a bit crowded and in some confusion over the placing 
of the rare earths? First, it was found that certain gas- 
eous ones belonged to the zero group. Then Soddy 
announced his theory of isotopes, namely, that there 
might be several elements which were so much alike 
chemically that they could not be separated by chemical 
means and yet differed in their atomic weights. Their 



NATURE OF THE ATOM 87 

chemical properties were to be taken as decisive and they 
belonged in one place in the system in spite of their 
atomic weights. Another contribution from radioactiv- 
ity was a method of deciding the location of an element 
by counting the recoil particles. A few years later Mose- 
ley, by his remarkable work in photographing X-ray 
spectra discovered a method by which this location 
could more easily and surely be settled. In this way 
were confirmed the exceptions made in the beginning 
in placing cobalt and nickel, etc. Fortunately in most 
cases the determining factor coincides with the atomic 
weight, or influence of mass. Otherwise the discovery of 
the Periodic System would have been long delayed. 
Composite Nature of the Atom. — The argimients 
in behalf of the composite nature of the elements may 
well be given here. When these arguments were duly 
weighed they caused more than a wavering in the old 
faith as to the simplicity of the elemental atom. The 
revelations of radioactivity have disclosed the internal 
structure of these particles so that they are known as no 
longer ultimate. Many chemists in the nineteenth cen- 
tury regarded the atom not as something which could 
not be divided but as something which had not been 
divided. A study of the Periodic System brought the con- 
viction that the elements were closely interrelated with 
constituents common to them all. Remsen wrote: ^'The 
so-called elements are shown to be related to one another 
and it seems impossible in the Hght of these facts to be- 
Ueve that they are distinct forms of matter. It seems 
much more probable that they are in turn composed 
of subtler elements.^' Gladstone, in an address before 
the British Association, said, *^The remarkable rela- 



88 HISTORY OF CHEMISTRY 

tions between the atomic weights of the elements and 
many pecuHarities of their grouping force upon us the 
conviction that they are not separate bodies created 
without reference to one another but that they have 
been built up from one another according to some general 
plan/' 

Evidence as to Complexity. — The first argument for 
complexity is drawn from the manifest kinship shown 
by the elements in the Periodic System. A second ar- 
gimient lies in the close analogies to be observed be- 
tween the compound radical NH4 and the alkaU ele- 
ments, the compound radical CN and the halogens, 
etc. These resemble elements in every respect except 
that they can be dissociated and built up at will. The 
presumption is strong that the same might be done 
for the other elements if only the suitable treatment 
were known. \ Again, it is known that when the va- 
lence of an element is changed the result is comparable 
to the formation of another element. The analogy 
to the homologous series of the hydrocarbons was pointed 
out by Cooke, Dumas, and others. Lastly, the number of 
lines found in the spectra of the elements can not well 
be referred to the motion of absolutely simple bodies. 
The matter has been finally settled by the phenomena 
of radioactivity, which have shown elements in the 
process of disintegration and new elements forming and 
have justified the conclusion that the atoms are made 
up of discrete units of positive and negative electricity 
and are, therefore, storehouses of enormous energy. ] 
So far, and one may add fortunately, no means of re- 
leasing this energy is at oirr command. Theories as 
to the structure of the atom and the disposition of this 



NATURE OF THE ATOM 89 

energy have been advanced by Rutherford, Bohr, Lang- 
mnir, and others. It will be seen that the Periodic Sys- 
tem thus receives its explanation and the series of ele- 
ments can be theoretically built up of the two simplest 
atoms, hydrogen and helium. This, however, is as yet 
only in a tentative stage. Valence and the electro-chem- 
ical characteristics also receive at least a rational ex- 
planation, whether final or not, and advanced chemistry 
has entered the sub-atomic or ultimate stage. 



CHAPTER XI 

AFFINITY, THE ATOMIC ATTRACTIVE FORCE 

It was seen from the very earliest times that the hy- 
pothesis of the atomic constitution of matter involved 
also an investigation as to the force which brought about 
the union of atoms and held them in combination. This 
was a problem which the earUest philosophers found 
themselves incapable of solving because of their general 
ignorance as to the natural forces and the paucity of 
their experimental or other data. 

The oldest idea as to the cause of the union of two 
substances was that they must contain some common 
principle. Thus Hippocrates (460-357 B.C.) taught 
as one of the fundamental doctrines that ^4ike would 
unite only with like.'^ This doctrine gave rise to the 
term used at present, affinity, though this ancient belief, 
cherished for centuries, has long since been lost sight of. 

The term afinitas seems to have been used first by 
Albertus Magnus to indicate the cause of the union of 
silver and other metals with sulphur. The same ex- 
pression was used by chemists following him and in 
very nearly the same sense as at present. Glauber, Boyle, 
Hooke, and others found it useful to designate the un- 
known combining force. Still it was inferred that some 
similarity must exist between the combining substances. 
The greater the affinity, the greater the resemblance. 
With the eighteenth century there came a change in 

90 



AFFINITY, THE ATOMIC ATTRACTIVE FORCE 91 

this beKef. Boerhaave sought to show that afl&nity was 
also evinced by dissimilar bodies in their tendency to 
combine. Solution was looked upon as an act of affinity. 
Boerhaave maintained that the solution of iron in nitric 
acid was also an act of affinity and that no relationship 
existed between the two, but that they were essentially 
different. His influence as a teacher and the wide dis- 
tribution of his text-books secured the introduction and 
general adoption of his views by chemists. Yet physicists 
opposed the idea of a new force. The term attraction 
used by Newton was too indefinite and general to displace 
affinity J which by that time had become fully incorporated 
into chemical literature, in spite of the recognition that 
the latter term was based upon a mistaken idea. 

Strength of Affinity. — The knowledge of this force 
grew very slowly. First, it was recognized that the 
force varied in strength. Glauber maintained that 
the tendency of one body to imite with another differs 
in accordance with the nature of the latter and that 
another substance can bring about the decomposition 
of such a union when it has a greater affinity for one 
of the components than they have for one another. And 
so it came about that two approximate tests were de- 
vised for measuring the strength of affinity. First, the 
readiness of combination and secondly, the displacement 
of one substance in combination with another. Obser- 
vations began to accumulate. Glauber and Stahl and 
others announced certain affinity series. In 1718 Geof- 
froy published sixteen tables, called by him tables des rap- 
ports, and then followed a number of tables by different 
chemists, the best and most widely known being the 
tables of Bergman in 1775. Bergman recognized the fact 



92 HISTORY OF CHEMISTRY 

that chemical affinity is influenced and varied by tem- 
perature, differing also with the physical state of the 
substances. Berthollet stated that it was affected by 
mass. He considered it as probably '^a phase of the 
same fundamental property of matter as that to which 
universal gravitation owes its origin. '^ The differences 
observable between the two he attributed to the prox- 
imity of the reacting substances in the case of affinity 
and to the influence of special conditions. BerzeHus 
offered as an explanation of affinity the hypothesis that 
it was dependent upon electrical attraction. This seems 
to have been first a conception of Davy. According 
to the thinking of BerzeHus, each atom is endowed with 
a certain quantity of electricity, partly positive and partly 
negative, which accumulates in particular parts of the 
atoms and gives to each a positive and a negative pole. 
The atom as a whole, however, has the character of 
either a positively or negatively electrified body be- 
cause of the preponderance of one or the other kind of 
electricity. When two atoms combine their respective 
charges are neutraUzed. Of course this offers an ex- 
planation of the greater attraction between unhke atoms. 
Every molecule then was built up of two parts, one 
positively and the other negatively charged, and thus 
formed a dual structure. The theory was known as the 
dualistic theory. In the imperfect knowledge of the 
day difficulties presented themselves, especially in the 
matter of the same element (as hydrogen) sometimes 
substituting a positive element and again a negative one, 
and hence the theory lost support. It is astonishing how 
closely it approaches the modern theory as to the con- 
stitution of the atom and attractive binding force. 



AFFINITY, THE ATOMIC ATTRACTIVE FORCE 93 

Measurement of Affinity. — Various attempts have 
been made at measuring the relative strength of affinity, 
but the many conditions which influence chemical re- 
actions and the lack of definite knowledge as to the 
nature of the force to be measured render the question 
a very complex one, and no satisfactory solution has been 
reached. The formation of a compound is accompanied 
by changes of energy; also the application of energy 
can cause the dissociation of a compound. It would 
seem to be simple to measure the energy liberated or 
appHed, but even then the results would be of little 
value unless the connection with affinity were accurately 
known. The part played by heat in reactions was, of 
course, a matter of early experience. The measurement 
of the heat evolved in chemical reactions has led to the 
development of the branch of chemistry known as thermo- 
chemistry. The first law discovered was that of La- 
voisier and Laplace, namely, that for the dissociation 
of a compound into its constituents the same amount of 
heat is absorbed as was evolved in its formation. This 
is true for endothermic reactions also where heat is ab- 
sorbed on combination and the same amount given off 
on dissociation. In 1840 Hess announced the impor- 
tant principle that in a chemical reaction the amount of 
heat evolved is the same whether the process takes place 
step by step or in one step. This removed many difficul- 
ties which lay in the way of the determination of this 
evolved heat. Thermochemistry was further built up by 
the work of Favre and Silbermann, and especially by 
that of Thomsen. It is possible to arrive at some knowl- 
edge of relative affinities by the study of analogous re- 
actions. Thus in the union of hydrogen with chlorine, 



94 HISTORY OF CHEMISTRY 

bromine, and iodine the heats of formation are respect- 
ively 44,000, 16,660, and 12,072 calories. These, how- 
ever, are not to be taken as proportional to the aflSni- 
ties involved but simply as varying in the same order. 
As Remsen says, ^'The difficulties are much increased 
in more complicated cases and it will, therefore, be seen 
that it is impossible to measure the affinity by means 
of the heat evolved in reactions/' 

Again, it would seem that there is some connection 
between this combining force and the electrical states 
of the atoms. Much stress has been laid upon this but 
Uttle is really understood concerning it. 

Valence. — Still another important property of the 
atom remains to be considered. This is called valence 
and is closely connected with the phenomena of affinity. 
Where there is no affinity between two atoms no valence 
can be exhibited. Valence decides the number of atoms 
which enter into a molecule. As both atoms have a def- 
inite valence, necessarily both have to be taken into 
account. The question of valence did not arise until 
there had been some development of the theories as to 
affinity. No necessity was felt for it until the number 
of known compounds had been greatly multiplied and 
the need for their classification became pressing. Valence 
has also been defined as the saturation capacity of the 
atoms. 

Evolution of the Idea. — Probably the first concep- 
tion of valence was in the recognition of the so-called 
polyatomic compounds. This term was first used by 
Berzelius in 1827, who applied it to such elements as 
chlorine or fluorine where he thought several atoms of 
these elements united with a single atom of another ele- 



AFFINITY, THE ATOMIC ATTRACTIVE FORCE 95 

ment. This use of the term does not seem to have re- 
ceived wide acceptance. It was applied to compounds, 
however, and for certain of these its use became general. 
Thus Graham applied it to the acids combining with 
various proportions of the bases. These were called 
polybasic acids. Odling and Williamson extended the 
idea to the compounds which, according to the theory 
prevailing at that time, were built upon types. Thus 
both the type theory of Laurent and the substitution 
theory of Dumas were involved in the evolution of this 
conception. The substitution of elements for one an- 
other would naturally lead up to the idea of the relative 
value of their atoms. This was called by Liebig the 
replacement value. The comparison between these 
atoms was inevitable, as they were generally substi- 
tuted for the same element — either hydrogen or oxygen. 
The quantities of the various elements thus substitut- 
ing hydrogen were regarded as the equivalents but when 
the confusion between equivalents and atoms was cleared 
up the pressing question became as to how many atoms 
were involved. 

The Organo-Metallic Compounds. ~ The important 
work of Frankland upon the series of organic substances 
containing metals, known as the organo-metallic bodies, 
had much to do with the clearing up of the confusion 
as to the saturation capacity of the atoms. This 
work showed that the pairing of the radicals with the 
elements was to be explained on the ground of some 
characteristic property of the atoms. Upon these ex- 
periments Frankland founded the valence theory, the 
germ of which one can detect in much that had gone 
before, especially in the law of multiple proportions; 



96 HISTORY OF CHEMISTRY 

but the idea had not been clear, nor even expressed in 
a name except by the vague term replacement value 
introduced by Liebig. 

Polybasic Acids. — What is known as the doctrine 
of the polybasic acids contributed to the growth of ideas 
upon the subject of saturation capacity. Gay-Lussac, 
GmeHn, and others had held the idea that in the me- 
talhc oxides one atom of metal was united with one atom 
of oxygen, and that these oxides united with one atom 
(molecule) of acid to form neutral salts. Graham showed 
by his investigations upon the acids of phosphorus that 
this view could be held no longer. He proved that in 
the ortho, pyro, and meta acids for each '^atom'' of 
P2O5 there were respectively three, two, and one ^^atom" 
of '^basic water,'' which could be substituted by equiva- 
lent amounts of metallic oxides. The saturation capac- 
ity of these acids was then dependent upon the ^^basic 
water.'' Liebig extended this to many other acids and 
distinguished between mono-, di-, and tri-basic acids. 
This term basicity, along with the ideas inherent in it, 
clung for some time to the theory of the saturation ca- 
pacity of the atoms. One sees in the above citation from 
the work of Graham the confused use of the term atom. 

Polyatomicity. — The idea of basicity was extended 
fiKther to the compound organic radicals. Thus Wurtz, 
in describing the glycerin compounds, wrote of glycerin 
as a tribasic alcohol. Manifestly there is confusion 
here since glycerin may combine with three acid radicals 
and the term should be triacid alcohol. The term ato- 
micity was, therefore, sometimes used. Williamson 
attached the idea of capacity for saturation or atomic- 
ity of the radical to the number of hydrogen atoms 



AFFINITY, THE ATOMIC ATTRACTIVE FORCE 97 

capable of substitution. He called these radicals then 
monatomic, diatomic, etc. Wurtz' study of the amines 
also bore upon this point and it is easy to see how the 
notion of atomicity was soon extended to the various 
compound radicals known. The last step was in the 
extension of this idea of satiu^ation to the elements them- 
selves. From their combinations and substitutions with 
these organic radicals their atomicity was deduced. 

Deduction of Valence from Inorganic Compounds. — 
When one considers the formulas of the inorganic chem- 
ical compounds even a superficial observer is attracted 
by the general symmetry to be observed in them. For 
instance, the compounds of nitrogen, phosphorus, anti- 
mony, and arsenic show a tendency on the part of these 
elements to form compounds in which either three or 
five equivalents of other elements are contained. With- 
out formulating an hypothesis to account for this agree- 
ment in the grouping of the atoms, it is clear that such a 
regularity exists and that the affinity of the atoms of the 
elements named is always satisfied by the same number 
of atoms. Frankland did not consider a higher valence 
than five. Though he mentioned the simple inorganic 
compounds and used them in illustration, he drew the 
valence doctrine from his studies of complex organic 
substances. 

Progress made. — The ideas advanced by Frankland 
did not meet with immediate acceptance. There was 
a somewhat prolonged discussion over the constitution 
of the polybasic acids and other compound groups, 
joined in by OdUng, WilUamson, Gerhardt, Wurtz, and 
others, which showed the necessity for a valence theory 
and did much to introduce it into the science. By 1858 



98 HISTORY OF CHEMISTRY 

the theory had made rapid progress. In this year Ke- 
kule j&rst deduced the valence of carbon from its sim- 
plest compounds, declaring it to be quadrivalent or capa- 
ble of combining with four hydrogen atoms. Hydrogen 
was taken as the standard or unit with a valence of one. 
On this basis an imvarjdng valence of four was assigned 
to carbon throughout all the compounds of carbon, or 
organic chemistry. This had already been recognized 
by Kolbe and Frankland, if not expressly stated by 
them. But Kekule rendered further and much greater 
service by examining into the manner in which two or 
more of the quadrivalent carbons were united with one 
another. The doctrine of atomic chains, open and closed, 
sprang from this and the domination of the structural 
idea in chemistry became complete. 

Following the example set in the compounds of carbon, 
it was the fashion for some decades afterwards to as- 
sign a single valence to each element and so construct 
the formulas of the compounds as to agree with this. 
The difficulties met with, and the glaring inconsisten- 
cies, caused this effort to be given up and brought about 
the recognition of the fact that an element might have 
more than one valence. Further, where the element 
has more than one valence the change from one to the 
other can be brought about by the application of energy, 
such as heat, light, chemical action, etc. It seems now 
that the explanation of the phenomena of valence is 
to come through the study of radioactivity. The modern 
conception of valence is an outgrowth of the knowledge 
of the electrical constitution of the atom and is based 
upon the existence of latent or valence electrons and 
their interchange. 



CHAPTER XII 

GROWTH OF INORGANIC CHEMISTRY 

It has been necessary to devote a good deal of time 
and space to the evolution of the fundamental theories, 
since growth in accurate knowledge and real progress 
depended upon these. They form the foundation of the 
modern science and a correct understanding of them, 
coming through a study of their development, is most 
important. It is well now to turn to the multiplication 
of chemical facts and enlargement of the field until 
the science of chemistry had to be subdivided into a 
number of branches. In the earlier half of the nine- 
teenth centiKy there was practically but one field and 
that was inorganic chemistry in which the metals and 
most of the elements are to be considered. The dis- 
covery of new elements is the first thing to attract the 
attention. 

Discovery of New Elements. — Among the early dis- 
coverers of new elements was the distinguished German 
chemist, Klaproth (1743-1817). It was largely through 
his influence that the German chemists were won over 
to the views of Lavoisier. He devoted himseK mainly 
to the analysis of minerals and the improvement of 
analytical methods. He added uranium and titanium 
to the list of simple bodies and discovered zirconia but 
was unable to separate the metal zirconium. Proust 
did accurate and valuable work in connection with the 

99 



100 HISTORY OF CHEMISTRY 

study of tin, copper*, iron, nickel, cobalt, antimony, 
silver, gold, and mercury, thus contributing to the ex- 
tension of chemical knowledge. But the two most 
distinguished discoverers in the first quarter of the 
nineteenth century were Davy and Berzelius. Their in- 
fluence upon the science has been very great and more 
extended mention is, therefore, accorded them. 

Humphry Davy (1778-1829). — The scientific train- 
ing of Davy was secured while apprenticed to a surgeon 
and apothecary at Penzance. At the age of twenty he 
was put in charge of the laboratory of the Pneumatic 
Institution at Bristol, founded by Dr. Beddoes for the 
application of gases to the treatment of diseases. Davy's 
surroundings here were most propitious for a successful 
career of scientific investigation. His laboratory was 
well furnished and was supported Ay the subscriptions 
of scientific men. His early experiments related chiefly 
to nitrogen monoxide. He discovered its anaesthetic 
action. While in this laboratory he gave some of his 
time also to experiments upon the decompositions brought 
about by means of electricity. Becoming professor of 
chemistry at the Royal Institution in London, he devoted 
himself to the decomposition of some of the substances 
then regarded as simple or elementary, among them the 
alkalis and alkaline earths. In this work he made use 
of a very powerful voltaic pile. 

Nicholson and Carlisle had made the observation 
in 1800 that water was decomposed into its constituents 
by the discharge from the voltaic pile. This led to simi- 
lar experiments upon other substances, among them the 
remarkable ones of Berzelius and Hisinger upon salt solu- 
tions, ammonia, sulphuric acid, etc. Davy was among 



GROWTH OF INORGANIC CHEMISTRY 101 

the first to busy himseK with this interesting and im- 
portant question, the decomposition of water. From 
the very first it was noticed that acid and alkahne sub- 
stances were formed and it was beheved by some that 
water was changed into these through the action of elec- 
tricity. By most careful experiments Davy showed the 
error of this view. He carried out this electrolysis in ves- 
sels of various materials and showed that the products 
mentioned, acid and alkah, were due to the glass ves- 
sels or to matter dissolved in the water or to the air 
itseK. If the water, distilled in silver, were electro- 
lyzed in gold vessels in an atmosphere of hydrogen the 
acid and alkah did not appear. 

Davy further repeated and confirmed the work of 
BerzeUus upon salt solutions. He, too, observed that 
the electric current separated hydrogen, metals, metal- 
lic oxides, alkalis, and earths at the negative pole and 
oxygen and the acids at the positive. He concluded 
that the first-named substances have a positive elec- 
trical energy and the latter a negative; and this was the 
beginning of the electro-chemical theory. Davy sought 
to explain all chemical combination and decomposi- 
tion on this principle. According to him, the heat noticed 
in certain cases of combination was due to and but a 
manifestation of electricity. Davy was the first to put 
in a fixed form the conception that electrical and chem- 
ical action may be referred to the same force. All the 
later doctrines that chemical changes are the evidences 
of electrical attractions take their rise from his work 
and views. 

Decomposition of the Alkalis. — In his first experi- 
ments upon potash and soda Davy used strong solu- 



102 HISTORY OF CHEMISTRY 

tions and noticed that only hydrogen and oxygen were 
evolved. He next passed the current through melted 
potash. A flame appeared at the negative pole and, 
on changing the direction of the current, ''aeriform 
globules which inflamed in the air rose through the pot- 
ash.'' When the potash was placed upon a piece of 
platinum, which was made the negative pole of a power- 
ful battery, and the positive pole, in the form of a plat- 
inimi wire, brought in contact with the upper surface 
of the potash the latter melted and small globules, lus- 
trous and metalUc and much hke mercury, were noticed 
on the negative platinum. Some burst and burned; 
others tarnished and became coated with a white film. 
Great was Davy's delight at his discovery, and one 
can scarcely exaggerate the impression made upon the 
chemical world by the decomposition of this supposed 
elementary body, and the remarkable new metal ob- 
tained from it. Its properties were quite the opposite 
of those which were held to be characteristic of the metals. 
It was Kght, oxidized immediately in the air, and contact 
with water brought about its decomposition. Davy 
also decomposed soda in a similar way, obtaining a 
metal with analogous properties. He confirmed his dis- 
covery by oxidizing these metals back into the original 
alkalis. He learned how to prepare larger quantities and 
to keep them under naphtha. He named these metals 
potassium and sodium. These discoveries were made in 
1807 and were followed next year by the decomposition 
of the alkaUne earths, Hme, baryta, and strontia. He 
was convinced by his experiments that siHca, alumina, 
zirconia, and beryllia could also be decomposed by the 
electric current but failed to obtain any of the supposed 



GROWTH OF INORGANIC CHEMISTRY 103 

elements existing in these substances. This he attrib- 
uted to his current not being powerful enough. Davy's 
discoveries confirmed the view, which was already widely 
held, that the alkahs and earths were metaUic oxides. 
It was not yet known that some of these were really 
the hydroxides. 

Composition of Muriatic Acid. — Davy's next impor- 
tant services were in connection with the theory of acids. 
BerthoUet, by his work upon hydrogen sulphide, hydro- 
chloric acid, and hydrocyanic acid, had really shown 
the imtenable character of Lavoisier's theory that oxy- 
gen was present in all acids and hence deserving of its 
name, the acid-maker. But Berthollet's experiments 
were not pressed to their legitimate conclusion and the 
theor}" of Lavoisier still held its place, though the ex- 
istence of hydrochloric acid became a serious stimabUng 
block. Ox^^gen, according to the theory, should be 
one of its constituents; yet no one could detect its pres- 
ence. If this acid contained ox}'gen, its salts should 
also. In 1774 Scheele had shown that by its action 
upon the black oxide of manganese a yellow, pungent- 
smeUing gas was obtained. BerthoUet showed that 
a solution of this gas in water gave off oxygen when 
exposed to sunhght, and hydrochloric acid was formed 
at the same time. Therefore, it was called ^^ oxidized 
muriatic acid." Muriatic acid was regarded as composed 
of ox^^gen and an unknown radical. These were not the 
views of Scheele, who called the gas ^^dephlogisticated 
muriatic acid'' and regarded it as hydrochloric acid 
deprived of its phlogiston or hydrogen. In 1809 Gay- 
Lussac and Thenard showed that one volume of '^ oxi- 
dized* muriatic acid" and one volume of hydrogen united 



104 HISTORY OF CHEMISTRY 

to form muriatic acid. This proved that it contained 
hydrogen. 

Davy next endeavored to find the oxygen which was 
supposed to be in this acid, but without success. He 
did show, however, that when ^^ oxidized muriatic acid'' 
acted upon metals salt-hke compounds were obtained, 
and that similar compounds, and at the same time water, 
were formed by the action of muriatic acid upon me- 
taUic oxides. Davy explained these results by regard- 
ing ^^ oxidized muriatic acid'' as an element and muri- 
atic acid as its compound with hydrogen, but chemists 
were slow to accept his views. Davy held that this 
element, to which he gave the name chlorine, resembled 
oxygen in many respects and in a hmited sense was 
also to be regarded as an acidifier and supporter of com- 
bustion. In the ensuing discussion with Gay-Lussac, 
who endeavored to prove from the work of Berzehus 
and Davy on ammonium amalgam and from the action 
of potassium on ammonia that hydrogen was an alka- 
hzing principle, Davy uttered the following important 
but often over-looked truth: '^The substitution of anal- 
ogy for fact is the bane of chemical philosophy; the 
legitimate use of analogy is to connect facts together 
and to guide to new experiments." 

Davy's facts were clear and convincing and in a few 
years chlorine was generally accepted as an element. 
In 1812 and 1813 iodine, discovered by Courtois, a French 
soap maker, and investigated by Gay-Lussac, was added 
to the list of acidifiers. 

The New Theory of Acids. — These additional facts 
necessitated a revision of the theory of acids. It came 
about that no one element was any longer regarded as 



GROWTH OF INORGANIC CHEMISTRY 105 

the acid-making principle but the acid properties seemed 
to be dependent upon the other element or elements 
combined with hydrogen. An acid might contain oxy- 
gen and be an oxy-acid or contain no oxygen. So, too, 
a salt might contain oxygen or, like the chlorides and 
iodides, have none in its composition. Thus the old 
view that a salt was a compound of the oxide of a non- 
metalhc element, or acid, and of the oxide of a metal, 
or base, was overthrown and salts came to be looked 
upon as metallic derivatives of acids, a metal replacing 
the hydrogen. The only element common to all acids 
was hydrogen. 

The Alkalizing Principle. — In this connection it is 
well to take up the discussion which arose as to the con- 
stitution of the alkaU metals, sodium and potassium. 
Davy had observed that these metals separated at the 
negative electrode, while oxygen appeared at the pos- 
itive when the hydroxide was electrolyzed; also that 
they had the power of reducing metallic oxides. He 
likewise showed that by their combustion in oxygen 
the alkahs seemed to be regenerated. Hence, he con- 
cluded, these substances were metallic and elementary. 
From his investigation of ammonium amalgam a little 
later he concluded that this was composed of mercury 
and a hypothetical metal-like substance, ammonium, 
which broke up into hydrogen and ammonia. The anal- 
ogy between this substance and the alkalis and the 
similarities between their amalgams gave rise to the 
theory that these alkali metals also were combined 
with hydrogen, a theory which Davy was more incUned 
to accept because of the combustibility of these metals. 
Gay-Lussac and Thenard had examined also the action 



106 HISTORY OF CHEMISTRY 

of potassium upon ammonia gas and noted the liberation 
of hydrogen and the formation of a green substance, 
the amount of hydrogen hberated being the same as that 
set free by potassium from water. From the green sub- 
stance they regenerated the original amount of ammonia 
used. Therefore, they said that potassiiun consisted of 
potash and hydrogen and that this hydrogen was set free 
by treatment with water or with ammonia. According 
to this theory, there was an alkalizing hydrogen. 

Davy soon returned to his original ideas as to these 
alkaU metals and gave as his explanation of the experi- 
ments of Gay-Lussac and Thenard that the hydrogen 
came from the decomposition of the ammonia and not 
from the potassium. In the year 1811 Gay-Lussac 
and Thenard came over to Davy^s views, having observed 
that the body obtained by burning potassium was not 
the same as potash but contained less oxygen, and that the 
melted potash w^as not water-free, as Davy.had imagined. 
Thus they gave up their theory that hydrogen was an 
alkahzing principle giving bases when combined with 
aromonia, soda, or potash and similar substances. 

Berzelius (1779-1848). — It was pecuharly fortunate 
for chemistry that two such briUiant and accurate in- 
vestigators as Davy and Berzelius should have appeared 
at a time when the framework erected by Lavoisier needed 
filling out and the foundations of the science had to be 
broadened and deepened. A succession of mediocre 
and inacciu'ate w^orkmen coming just then would have 
more easily misled and more seriously retarded the 
science than at a later period. Berzelius ranks as one 
of the greatest of chemists and the chemists of to-day 
can scarcely overestimate their indebtedness to him. 



GROWTH OF INORGANIC CHEMISTRY 107 

Berzelius was born in Sweden one year after the birth 
of Davy. Poverty greatly hampered both in their younger 
years and both were forced to follow medicine and phar- 
macy as a means of Kvehhood at first. Berzehus became 
professor of chemistry in Stockholm. Here he lacked 
the apphances and the leisure afforded Davy by his 
freedom from class work. Still, his lectures and classes 
enabled Berzehus to impress himseK and his views upon 
the rising generation of chemists, and some of the noted 
chemists received training under him. His career was 
fiu'ther comparable to that of Davy in that he held an 
honored post, namely, that of permanent secretary to 
the scientific society of his native land and was ennobled 
by his king. 

Contributions of Berzelius. — It is difficult to give 
a short and at the same time fair account of the work 
of this great man, as it covered nearly the entire field 
of chemistry and hence was of the most varied and ex- 
tensive character. Only brief reference can be made to 
some of the more important work. It is interesting to 
note the difference between the equipment with which 
this work was done which compares but poorly with the 
expensive apphances and large means which were at the 
command of Davy and increases the wonder over what 
he accompUshed. Wohler, his most distinguished pupil, 
has left a description of his first visit to the laboratory 
of Berzelius in which so many famous discoveries had 
been made. 

^'No water, no gas, no hoods, no oven were to be seen; 
a couple of plain tables, a blow-pipe, a few shelves with 
bottles, a httle simple apparatus, and a large water- 
barrel whereat Anna, the ancient cook of the estabUsh- 



108 HISTORY OF CHEMISTRY 

ment, washed the laboratory dishes, completed the 
furnishings of this room, famous throughout Europe 
for the work which had been done in it. In the kitchen 
which adjoined and where Anna cooked was a small 
furnace and a sand-bath for heating purposes." 

At the time of Davy and BerzeHus the chemist was 
expected to be something of a mechanic, able to cut 
and form, fashion and solder, the wood, brass, and iron 
into the various shapes he needed. He must also have 
skill as a glass blower, for in most cases he would have 
to depend upon his own cunning of hand for the success 
of his experiments. 

Analytical and Experimental Work. — Berzehus in- 
troduced many improvements in the methods of ana- 
lytical chemistry, devising new means of separating and 
determining the different elements. His close attention 
to details led him to the discovery of selenium, ceria, 
thoria, and many new compounds. He was also the 
first to prepare the elements sihcon, zirconium, and a 
pm*er tantalum, and did much towards enlarging the 
knowledge of the platinum metals. He made a great 
nmnber of investigations to prove the law of constancy 
of proportions and also Dalton's law of multiples. He 
enriched mineralogy by many analyses of minerals and 
showed that minerals were simply naturally occurring 
chemical compoimds which obeyed the ordinary laws 
of combination. He introduced a chemical system 
for the classification of minerals based upon this view 
of their nature. He extended the law of multiple pro- 
portions to organic chemistry and did much to system- 
atize that branch of chemistry. 

Determination of Atomic Weights. — BerzeHus, to- 



GROWTH OF INORGANIC CHEMISTRY 109 

gether with the pupils in his laboratory, undertook the 
determination of the atomic weights. The analytical 
work, of course, greatly excelled in accuracy that of 
Dalton, and in the rules laid down for guidance in de- 
ciding the number of the atoms in a given compound 
or molecule he showed a far greater knowledge of and 
insight into chemical reactions. Still his rules were 
in some respects arbitrary and unsatisfactory. By re- 
calculating the results from his analytical data many 
of his determinations have been cited and utihzed in 
settling these physical constants in the centinry which 
has elapsed since his time. It has already been men- 
tioned that in 1813 this far-seeing man recognized in 
part the distinction made by Avogadro between atoms 
and molecules. His first fairly complete table of the 
atomic weights was published in 1818. 

Introduction of Symbols. — The rapid development 
of the science made it necessary to have some short- 
hand method of recording elements, compounds, and 
reactions. Of course a few symbols taken from ancient 
mythology, astrology, etc., had been used by the al- 
chemists and iatro-chemists, and there were later spo- 
radic efforts at shortening the record. Dalton, for in- 
stance, had attempted to introduce certain diagramatic 
symbols but failed because of their unpractical nature. 
Thus, oxygen was a circle O ; hydrogen, a circle enclos- 
ing a dot, O ; and water became O O . Carbon was a 
solid black circle, • and carbon dioxide, therefore, was 
O • O . And so the hst went on with large circles, barred 
circles, radiated circles, etc. 

BerzeUus greatly aided the progress of chemistry by 
the introduction of a rational, simpUfied set of symbols. 



110 HISTORY OF CHEMISTRY 

the meaning of which was caught at a glance. The 
system was practically the same as that which has been 
in use ever since. He proposed that the first letter of 
the Latin name of the element should be used to desig- 
nate it and that this should represent one atom, or equiv- 
alent of it. A compoimd was represented by placing 
the proper number of these symbols side by side. Thus 
H is hydrogen, CI is chlorine, and HCl is hydrogen • 
chloride. He supposed the existence of certain double 
atoms where two atoms of an element occur together. 
These were indicated by a mark across the sjTubol; 
thus HO was water, or, as it is written now, H2O. For 
convenience sake an atom of oxygen was often indi- 
cated by a dot, an atom of sulphur by a mark at right 
angles. Thus carbon dioxide C; potassiimi nitrate, KN. 
The Dualistic Theory. — In matters of theory Ber- 
zeUus exercised also a commanding influence. The 
combining power of the atoms he attributed to their 
electro-chemical character, his view of the atom being 
that it carried a distinct charge. The term atom was 
extended by him to include what he looked upon as 
compound atoms. These were built up of two parts, 
each of which might be a simple atom or several atoms 
in which each of the two parts acted as a single, sim- 
ple atom. This was the dual structure and formed the 
duaUstic system of BerzeUus. This theory has already 
been referred to and is mentioned again because of the 
system of writing formulas of compounds which he 
introduced and which was in vogue for many years. Thus 
barium sulphate was supposed to be made up of barium 
oxide and sulphur trioxide, the first positively charged 
and the latter negatively charged. The formula was 



GROWTH OF INORGANIC CHEMISTRY 111 

written BaO.SOs. So also CaO.COs, ZnO.SOs, etc. 
To write such formulas correctly required a knowledge 
of the valences, both of atoms and compound radicals, 
which was lacking at that time. 
' Additions to the List of Elements. — During the pe- 
riod covered by Berzehus several new elements were 
discovered by his pupils and others. In 1817 Stromeyer 
discovered cadmium and in the same year Arfvedson 
announced the separation of lithium. In 1828 Wohler 
succeeded in obtaining aluminum, beryllium, and yt- 
trium. Some years later Mosander separated several of 
the metals contained in the rare earths, as lanthanum, 
erbiimi, and terbium. Bussy separated magnesiimi in 
1829; vanadium was added by Sefstrom in 1830. The 
first of the platinum metals was discovered by Wood 
in 1741 and the last of these, ruthenium, was separated 
more than a century later — in 1845 — by Claus. No 
further discoveries were made until the spectroscope was 
brought into use. By its aid in 1860 Bunsen added two 
new elements, rubidium and cesium, and more than a 
dozen have been found since. This deHcate means of 
testing also revealed the fact that while many of these 
new elements constituted a very small proportion of 
the substances making up the crust of the earth they 
were very widely distributed; and furthermore, that the 
sun and other celestial bodies were composed of the 
same sort of matter as was to be found on our planet, 
and so the universe was one harmonious whole as to 
composition and governed by the same laws. The fact 
that each element has its distinctive spectrum fur- 
nished a final test as to whether or not the substance 
under examination was really a new element. Depend- 



112 HISTORY OF CHEMISTRY 

ence upon chemical methods and tests alone caused 
many mistakes and something like a hundred false an- 
nouncements have appeared in chemical literature. 

The Monatomic Gases. — Great interest was aroused 
when Ramsay and Rayleigh discovered argon in 1894, 
and also a few years later when Ramsay announced 
the existence of its companion gases, helium, neon, 
krypton, and xenon, all of which are found in the at- 
mosphere. The story of the discovery illustrates well 
the value of careful and accurate work without neglect- 
ing apparently trivial details and the following up of 
each clue until, so far as possible, everything is known 
and understood about the subject under investigation. 
It is sometimes stated that discoveries and important 
advances are often brought about through accident. 
Thoroughness does not admit of accident. It would 
seem more fitting to reserve the term for the one who 
had his chance and missed it. The opportunity passes 
and may never return. There have been many such un- 
happy instances in science. 

In his analytical examination of air in 1785 Caven- 
dish subjected an enclosed volume to the action of the 
electric spark. Oxygen was added from time to time 
until there was more than enough to combine with all 
of the nitrogen. The products and the excess of oxygen 
were removed by solvents. It is a testimony to the ac- 
curacy both of his observation and reporting of details 
that he recorded the presence of a residue or bubble, 
equal to about -rko of the original volume. Many others 
made use of this method and either failed to note or to 
report the residue, and no attention was paid to the 
observation of Cavendish. 



GROWTH OF INORGANIC CHEMISTRY 113 

More than a century later (1894), while determining 
the density of nitrogen, Lord Rayleigh found that there 
was a difference between the density of that prepared 
from the compounds of nitrogen and the nitrogen ob- 
tained from air, the latter being haK a per cent heavier. 
This brought to mind the forgotten observation of Caven- 
dish and led to an examination of air to see whether it 
contained any unknown gas. The investigation was 
carried on jointly by Rayleigh and Ramsay, who pursued 
different methods for removing the nitrogen from the 
air, and their results agreed. The air contained a gas 
which would not combine with anything else and to 
this new element the name argon was given. It forms 
about one per cent by volume of the atmosphere and 
can therefore be prepared from it in large quantities. 
It has no combining power and its molecule consists of 
a single atom. It has its distinctive spectrum and can be 
detected by this means. 

In the following year Ramsay examined a strange 
gas which had been reported as present in certain ura- 
nium minerals, thinking that this also might prove to be 
argon. He found the spectrum to be quite different 
and identified it with the spectrum of one of the ele- 
ments found in the sun some thirty years earUer by 
Lockyer and named by him helium. In the uranium min- 
erals the helium occurs along with small amounts of 
nitrogen and argon. It is known now to occur in the 
atmosphere, in well and spring waters, and in the natural 
gas which is drawn from the earth in many places. This 
also is a monatomic gas and forms no compounds. Hy- 
drogen and helium are the lightest gases known and, next 
to hydrogen, heUum has the lowest atomic weight and is 



114 HISTORY OF CHEMISTRY 

the most difficult of the gases to Hquefy. These facts 
have their bearing on the latest theory of the composi- 
tion of the atoms. 

Many other minerals were examined by Ramsay, but 
no further new gases were obtained from them. A more 
exhaustive study was then made of the air, in which 
Travers assisted Ramsay. The method was to take very 
large quantities of Hquid air and examine the fractions 
which evaporated at different temperatures. In this 
way, in 1898, they succeeded in separating three new 
elements to which the names neon, krypton, and xenon 
were given. These resembled heHum and argon and 
belonged to the monatomic group. Later Moore made 
a still more thorough examination, evaporating one hun- 
dred tons of liquid air, but found no additional new 
gases. 

Further Developm.ent of Inorganic Chemistry. — Dur- 
ing the century which has elapsed since Berzelius be- 
gan his most important work a great many able chem- 
ists have labored in the field of inorganic chemistry; 
multitudes of new compounds have been formed and 
studied and a better understanding reached as to the 
laws governing their formation and decomposition. 
It is in this way that science grows — an army of toil- 
ers in the ranks, a good and competent captain here and 
there, and, when the emergency arises, a great strat- 
egist who leads the way to masterful accomplishment 
— a Newton, a Lavoisier, a Dalton, a Berzelius, a Fara- 
day, a Mendeleeff. History cannot tell the story of 
all, but each faithful private in the ranks deserves his 
meed of gratitude. 



CHAPTER XIII 

DEVELOPMENT OF ORGANIC CHEMISTRY 

In the text-book of Lemery, in use in the latter half 
of the seventeenth century, all chemical substances 
were classified and separately treated under the three 
headings, mineral, vegetable, and animal substances. 
This division seems to have been made first at this time 
and was the usual one during the next century. This 
corresponded with the favorite grouping of the ^Hhree 
natural kingdoms^' which was so much used in books 
on general science a few generations ago. It was the 
animate and inanimate creation, and between the two 
lay the barrier of hfe or vital force which was not to be 
transcended. So chemists chiefly busied themselves 
with the mineral world, its compounds and elements 
and the wonderful laws governing them, and through 
their study reached down to the unchanging atoms 
upon which they founded their faith and their working. 
A building on any other foundation was as futile as a 
building on the sand. 

The Views of Lavoisier. — Here also the master mind 
came to the rescue. Beginning with the foundation of 
stones, Lavoisier showed that all of these products of life 
processes were composed mainly of carbon, hydrogen, and 
oxygen. Some included nitrogen and still fewer contained 
phosphorus and sulphur. Before this there was great 
doubt and discussion as to their composition, but Lavoisier 

115 



116 HISTORY OF CHEMISTRY 

showed how they could be analyzed with fau- accuracy. 
Quite so, one might say and many did say, you can 
tear down and find of what the building was made but 
you can never rebuild. Only this strange, evasive, im- 
knowable vital force can do that. Had man halted, bhnd 
and impotent, before that man-erected barrier he would 
have been without most of the comforts of modern life, 
and it is doubtful whether the huge population now 
inhabiting the earth could exist. Chemistry is not merely 
analytical but creative, and so chemists began to regard it. 
Lavoisier devised a system of quantitative analysis for 
these substances so as to decide their composition fully. 
Acid substances were recognized among them and La- 
voisier accounted for their nature by supposing that in 
these cases the oxygen was combined with a compound 
radical or organic residue. This idea was later developed 
by Berzehus and his followers until organic chemistry 
became the chemistry of the compound radicals. But 
the first tearing down of barriers came when that erected 
between the ^'vegetable and animal kingdoms^' was 
overthrown through the investigation of the fats by 
Chevreul. These fatt}^ substances are found in both 
plants and animals and Chevreul proved that many of 
them were identical. He also showed that the same was 
true of certain acids and other substances. So the first 
part of the distinction was no longer tenable, but the line 
was still very sharply drawn between mineral substances 
and the products of plant and animal life. These latter, 
it was beheved, could not be artificially formed out of 
the elements that composed them. They were produced 
by. some mysterious force, life, whose operations could 
not be imitated. The ordinary laws governing chemical 



DEVELOPMENT OF ORGANIC CHEMISTRY 117 

affinity could not be expected to apply in this field and 
chemical theories could not explain the phenomena 
of Hfe. 

Views of Berzelius. — In 1811 Berzehus attempted 
to prove that organic substances were nothing more than 
ordinary chemical compounds, obeying the laws of con- 
stant and multiple proportions and offering a fair field 
for the application of the atomic and other theories. 
With improved apphances and analytical methods he 
succeeded in showing the correctness of his views, but 
only after years of labor. In the third decade of the cen- 
tury he came to look upon organic substances as composed 
in the same way as the inorganic compounds but having 
compound radicals in the place of elements. With a 
satisfactory definition of compound radical this is the 
basis of organic chemistry, though much work had to 
be done before it was made clear. Berzelius attempted 
to apply his duahstic theory to the compound radicals 
which were recognized by him. He was in a measure 
led to take up this idea of the compound radical by the 
research of Gay-Lussac upon cyanogen, in which he 
showed that this radical behaved like an element. At- 
tempts were multiplied to discover the various organic 
substances which had complex groupings of atoms and 
functioned as elements. Thus Gay-Lussac looked upon 
alcohol as ethylen and water. Dobereiner regarded oxahc 
acid as carbonic acid and carbon monoxide. Berzehus 
pointed out that this was in contradiction to the electro- 
chemical theory. There was danger of confusion and error. 

Isomerism. — The search for the proximate constit- 
uents in organic compounds brought about a rapid 
development of the science. There were many efforts 



118 HISTORY OF CHEMISTRY 

at settling the chemical constitution of these substances. 
One of the important discoveries made was that of isom- 
erism. This was at first looked upon as an error, so 
Uttle were chemists prepared to beheve that substances 
similarly composed could be chemically and physi- 
cally different. It was in the year 1823 that Liebig an- 
nounced that his analysis of silver fulminate yielded the 
same results as Wohler had obtained in the preceding 
year for his silver cyanate. He was confident that his 
figures were correct and believed that Wohler must have 
made a mistake. A careful repetition of the analyses 
showed him that both were correct. Thus it was proved 
that two substances, totally unlike, could and did have 
the same composition. Gay-Lussac saw that the only 
explanation of this lay in the different mode in which the 
elements were united with one another. BerzeUus hesi- 
tated to accept the facts or any generalization from them. 
Then followed in 1825 Faraday's discovery of an isomer 
of ethylen chloride, and in 1827 Wohler's transformation 
of ammonium cyanate into urea. BerzeUus himself showed 
the isomerism existing between tartaric and racemic 
acids, and chemists became accustomed to the new fact 
of isomerism for the explanation of which the atomic 
theory is so necessary. BerzeUus suggested the name 
isomerism. He also adopted as the most plausible ex- 
planation of isomerism the different arrangement of the 
atoms. He seems to have thought it a possibiUty to 
determine the mutual relations of the atoms in their 
compounds, or the manner in which the atoms were united 
to the compound radicals or proximate constituents. 

The Synthesis of Urea. — Many of the naturaUy 
occurring minerals had been reproduced or synthesized 



DEVELOPMENT OF ORGANIC CHEMISTRY 119 

by the chemist, but it was still a common beHef that 
the synthesis or imitation of organic substances was 
beyond the reach of experimental methods, as they were 
the products of life itseK and could be formed only in 
the plant or animal tissue. It is true that new organic 
preparations had been made by distilUng or otherwise 
treating various products of plant life but the original 
source or starting point remained the same hfe products. 
Chevreul had shown that the natural fats were com- 
pounds of certain acids and the glycerin discovered by 
Scheele, but no one had built up these two components. 

It was Wohler's brilhant synthesis of urea which 
finally broke down this barrier, proving the forerunner 
of many syntheses and inciting numbers of chemists to 
engage in such interesting and valuable work. It was 
in 1828 that he undertook to prepare ammonium cyanate 
by evaporating a solution containing ammonium sul- 
phate and potassium cyanate. The evaporation yielded 
crystals of urea instead. The same change will take 
place if a solution of ammonium cyanate alone is evapo- 
rated. This contains the same elements and the same 
number of atoms as are present in urea. Heating the 
solution brings about a rearrangement of the elements. 
Thus NH4CNO becomes (NH2)2CO. The cyanates were 
supposed to belong to the inorganic compounds and could 
be prepared from the elements. Hence the synthesis 
was\omplete without the intervention of a hypothetical 
vital force. Urea is one of the most interesting and best 
known of animal products, being the compound in which 
most of the waste nitrogen is eliminated by animals, 
and no more striking example of the fallacy of the old 
assumption could have been chosen. While the dying 



120 HISTORY OF CHEMISTRY 

away of the old belief was not immediate, Wohler^s 
discovery is commonly pointed to as marking the begin- 
ning of organic chemistry as a distinct branch of the 
science. 

Organic Analysis. — One obstacle to the rapid de- 
velopment of this branch of chemistry lay in the imper- 
fection of the analytical methods. Lavoisier had laid 
the foundations for the correct analysis of organic sub- 
stances and Gay-Lussac, BerzeUus, and Dobereiner had 
successively improved the processes. However, the oper- 
ations were still slow, difficult, and not very accurate. 
In 1830 Liebig greatly improved the methods of analysis 
and his processes have not needed very many nor great 
modifications to fit them to the needs of the present day. 
Of course, as the years passed gas and electricity sup- 
planted the charcoal which he used for heating. Im- 
proved methods for determining the halogens, nitrogen, 
vapor densities, etc., were introduced by Carius, Hofmann, 
Victor Meyer, and others, so that extremely accurate 
work can now be done. 

Classification of Organic Substances. — A true and 
helpful classification of these substances, the known 
number of which was increasing so rapidly, was lacking. 
In 1811 Gay-Lussac and Thenard, interpreting the results 
of their analyses, had divided them into three classes: 

1. Those which contain just so much oxygen as is 
necessary to form water with the hydrogen present. 
These were carbohydrates. 

2. Those containing less than that porportion of oxygen. 
These were the resins and oils. 

3. Those containing more oxygen. These were con- 
sidered the acids. 



DEVELOPMENT OF ORGANIC CHEMISTRY 121 ! 

Of course, so primitive and faulty a classification as 
this was of Little service. For instance, it quite ignored 

the many hydrocarbons which contain only carbon and j 

hydrogen. It merely serves to show that in the formative I 

stage of the conceptions held as to these substances no j 

satisfactory classification was possible. j 

Extension of the Electro-Chemical Theory. — In 1819 I 
Berzelius declared that his electro-chemical theory could \ 
not be extended to organic chemistry, as here these \ 
elements were under the influence of life force. In decay, I 
fermentation, etc., he saw evidences of a striving on the ; 
part of these elements to return to their normal con- J 
dition. He later extended both this theory and that of | 
duahsm to this branch of chemistry, seeing in the com- 
pound radicals the same dualistic condition which he ! 
thought existed in what he called the compound atoms of - 
inorganic substances. 

Extension of the Radical Theory. — There was con- 
tinued effort at extending the radical theory to organic ' 
chemistry. Thus in 1828 Dumas announced that ethylen 
was such a radical and gave a table of its compounds, 
endeavoring to show their analogy to ammonia and its j 
compounds: I 

defiant gas or ethylen, 2C2H2; NH3, ammonia. ; 

Hydrochloric acid ether, 2C2H2.HCI; NH3.HCI, ammonium ' 

chloride. 

Ether, 4C2H2 . H2O ; 2NH3 . 2H2O, ammonium oxide. 1 

Alcohol, 4C2H2.2H2O. i 

Acetic ether, 4C2H2.CsH6O3.H2O; 2NH3 . CsHeOs . H2O, am- I 

monium acetate. 
Oxalic ether, 4C2H2.C4O8.H2O; 2NH3.C4O8.H2O, ammonium 

oxalate. < 



122 HISTORY OF CHEMISTRY 

It was a part of this theory that the radicals could be 
separated and were capable of independent existence. 
This was called the Aetherin theory and was largely 
based on the ease with which alcohol could be converted 
into ether and ethylen. In this the aetherin C4II4 was 
a base, forming hydrates with water and salt-like ethers 
with acids. This must serve as an illustration of the im- 
perfect attempts at discovering these radicals and the 
great difficulties attending such researches. 

The Benzoic Acid Radical. — The radical theory 
received its greatest support from the classical research 
of Liebig and Wohler in 1832 On the Radical of Benzoic 
Acid. This was hailed by Berzelius as heralding the 
dawn of a new day. It was at least an epoch-making 
contribution, standing out as a masterpiece amid much 
that was erroneous and misleading in the work of the day. 
These two great chemists, then young men, showed that 
in the oil of bitter almonds (benzaldehyde) and its many 
derivatives one group of atoms remained unchanged 
and characterized the whole. This they called benzoyl 
and assigned to it the formula C14H10O2, or the present 
formula doubled. Benzaldehyde itself was this radical 
with hydrogen, C14H10O2+H2; the radical plus oxygen 
was benzoic acid; with chlorine it was benzoyl chloride, 
etc. 

Changes in the Radical Theory. — This briUiant re- 
search aided greatly in the advancement of organic chem- 
istry by the valuable new methods of research which it 
introduced into the practice of the chemist. Furthermore, 
a new principle was recognized. Hitherto it had been 
thought necessary to isolate the radical, and it was the 
great difficulty or even impossibiUty of doing this that 



DEVELOPMENT OF ORGANIC CHEMISTRY 123 

rendered much of the work futile. Benzoyl had not 
been isolated and was not known except in compounds, 
but one could as Uttle afford to doubt its existence, 
since its compounds were known, as to question the ex- 
istence of magnesiima or aluminum, whose compounds 
were well known a long time before the metals them- 
selves were separated. Thus chemists were aroused to 
search for the common radicals in substances which 
showed by their chemical behavior or modes of prepara- 
tion that they should be grouped together. 

Berzehus and Liebig entered upon this work with 
much success. The difficulty in recognizing benzoyl as 
a radical because of its containing oxygen was done away 
with by regarding it as the oxide of the real radical. The 
early idea of a radical was that it was a compound of car- 
bon and hydrogen only and contained no ox^^gen. Thus 
ether was the oxide of the radical ethyl, but Berzelius 
missed the connection with alcohol by regarding that 
as the oxide of the radical C2H6. This was corrected 
by Liebig, who, however, doubled the formula of the 
radical ethyl C2H5. So for him alcohol was the hydrate 
of ethyl C4H10O.H2O. 

Chemists agreed as to the existence of compound radi- 
cals in these various compounds. It is not surprising 
that they should differ as to the nature of the radicals 
themselves when one considers that this was really only 
the beginning of organic chemistry and the knowledge of 
these substances was very imperfect. Berzelius was in- 
clined to the belief that these radicals were unchangeable. 
Liebig took a wider view of them, looking upon his group- 
ing of the elements merely as a means to a better under- 
standing of the transformations these bodies imdergo. 



124 HISTORY OF CHEMISTRY 

But despite minor differences, the brilliant chemists who 
have been cited had obtained an insight into the basic 
principles of classification for organic substances. The 
hydrocarbons do fimction here as the elements and do 
form compounds which correspond to the hydroxides, 
oxides, haUdes, sulphides, etc. But since they themselves 
are capable of combination and change there is a be- 
wildering versatiHty and great multipHcation and com- 
plexity of the compounds formed. 

Compound Radicals. — About 1837 this theory of the 
compound radicals reached its highest point of credit and 
influence, and organic chemistry became the chemistry 
of the compound radicals. Liebig and Dumas united in 
valuable investigations, and a citation from a joint pub- 
lication of theirs will serve to show how far they carried 
the classification: 

" Organic chemistry possesses its own elements, play- 
ing at one time the role of chlorine or oxygen, at 
another that of a metal. Cyan, benzol, amide, the 
radicals of ammonia, of the fats, of alcohol, form the 
true elements of organic nature; whilst the simplest con- 
stituents, as carbon, hydrogen, oxygen, and nitrogen 
become recognizable only when the organic material 
has been destroyed.'' 

A year later Liebig clearly defined a compound radical, 
giving three essential characteristics and using cyanogen 
as a type: 

1. We call cyan a radical because it is an unchanging 
constituent in a series of substances or compounds. 

2. Because it can be substituted in these by other 
simple bodies. 

3. Because in its compounds with a simple body 



DEVELOPMENT OF ORGANIC CHEMISTRY 125 

this last can be separated and substituted by another 
simple body. 

At least two of these conditions must be fulfilled for 
a group of atoms to be regarded as a radical. 

This radical theory aroused great interest and stimu- 
lated chemists to much fruitful and even brilliant work. 
Special mention may be made of the research of Bunsen 
upon the kakodyl compounds which formed, indeed, one 
of the strongest supports of the theory. 



CHAPTER XIV 

FURTHER THEORIES AS TO STRUCTURE 

Atomic Theory Confirmed. — The duaUstic theory 
and that of the compound radicals were necessarily 
founded upon the atomic theory of Dalton. As they 
were discussed and struggled over and became intrenched 
in the science they rendered the atomic theory an indis- 
pensable assumption. Even when duaUsm became dis- 
credited and organic chemistry took on a different sig- 
nificance from that of the chemistry of the compound 
radicals atoms were still necessary, and the only possible 
changes were in the conceptions of the nature of the ulti- 
mate particles. 

Substitution Theory and Overthrow of Dualism. — 
Doubts began to arise as to the theory of duahsm. Du- 
mas and other chemists felt that Berzehus had pressed 
his theory too far. It was, however, the discovery of the 
principle of substitution which really dealt this theory its 
deathblow and paved the way for the so-called unitary 
theory. Substitution might have been deduced from the 
old idea of equivalence. It was also touched upon in the 
researches of Mitscherhch upon isomorphism. Other 
facts led up very nearly to it. But, as so often happens, 
the thought and its suggestion were brought about through 
an accident. 

Substitution of Chlorine for Hydrogen. — In 1834 Du- 
mas was called upon to examine into the cause of certain 

126 



FimTHER THEORIES AS TO STEUCTUHE 127 

irritating vapors coming from wax candles used to illu- 
minate the Tuileries. He found that in bleaching the wax 
chlorine had been used and some of the chlorine remaining 
in the candles had caused the disagreeable fumes. These 
consisted of hydrogen chloride, the hydrogen coming 
from the wax. Dimias felt that this could not be ex- 
plained on the ground of a mechanical retention of the 
chlorine as an impurity. He then fully investigated the 
action of chlorine upoa wax and kindred organic sub- 
stances. He found as a result of his investigations that 
hydrogen in organic compounds may be exchanged for 
chlorine, volume for volume. Wohler and Liebig had 
shown in 1832 that in preparing benzoyl chloride out of 
oil of bitter almonds by the action of chlorine two atoms 
of chlorine took the place of two atoms of hydrogen. 
This was contrary to the central idea of duaUsm, since 
chlorine was electro-negative and should never substitute 
electro-positive hydrogen. Additional facts accumulated. 
Liebig had shown that by the action of bleaching powder 
and chlorine upon alcohol chloroform and chloral were 
formed. He misunderstood the constitution of these 
compounds but Dumas determined correctly their con- 
stitution and their relation to alcohol, showing here the 
far-going substitution of chlorine for hydrogen. 

Trichloracetic Acid. — Dumas by his substitution of 
chlorine for hydrogen in acetic acid, forming trichloracetic 
acid, secured the most important support for his theory 
of substitution. It can be seen from what he wrote re- 
garding this acid what his views were as to substitution, 
and how the discovery of the acid supported them. In 
trichloracetic acid there are three of the hydrogen atoms 
of acetic acid substituted by chlorine. 



128 HISTORY OF CHEMISTRY 

"It is a chlorinated vinegar/' says Dumas, "but it 
is remarkable, and the more so for those who dishke to 
find in chlorine a body capable of substituting hydrogen 
in the exact and full sense of the word, that this chlorinated 
vinegar is still an acid hke ordinary vinegar. Its acid 
power has not been changed. It neutraUzes the same 
amount of base as before. It possesses the same acidity 
and its salts, compared with the acetates, show an agree- 
ment full of interest. '' 

Thus it was shown that the views of duaUstic structure 
were too rigid and a hindrance to the development of 
organic chemistry. A negative atom could be substituted 
for a positive and the compound radical began to be re- 
garded as an atomic structure in which one atom could 
be substituted for another without regard to its electro- 
chemical nature. Laurent showed that Dumas' state- 
ment as to substitution did not hold good for all cases. 
Often more chlorine was taken up, and sometimes less 
than corresponded to the volume of hydrogen lost. As 
the substituted body showed certain analogies to the 
original, he maintained that the chlorine took the place 
held by the hydrogen in the molecule and, to a certain 
extent, played the same role. 

Unitary Theory. — The views as to substitution met 
with vigorous opposition and had to be modified in some 
particulars, but soon the molecule came to be regarded 
as a unitary and not a dualistic structure. Thus there 
were two opposing theories: The older, dualistic, looked 
upon the molecules as double natured and composite 
yet forming one unchangeable whole in which the members 
lost their individuaUty and the nature of these molecules 
was determined by the quality of the atoms; the new, 



FURTHER THEORIES AS TO STRUCTURE 129' 

unitary, theory maintained that the niunber of the atoms 
and their arrangement determined in the main the nature 
of the compound, and that this molecule was not un- 
changeable but that the atoms comprising it could be 
substituted by others without a complete change of nature. 

Nucleus Theory. — Laurent was led to propound 
further the nucleus theory which was largely adopted. 
This was in some respects an elaboration of the compound 
radicals. Many of the ideas in this theory have been 
incorporated in the science, though the theory itseK 
has been dropped. This theory sprang from the old radical 
theory but with an important difference, i.e., the radical 
here is not an unchanging group of atoms but a com- 
bination which can be changed through the substitution 
of equivalents. It is but a step in the evolution of the 
modern theory, as seen in the benzene nucleus. 

T3^e Theory. — The idea of types was introduced 
by Laurent and Gerhardt and was appHed to both in- 
organic and organic chemistry. It was rapidly taken 
up and became the dominant structural theory of chem- 
istry in the fifth decade of the nineteenth century. Ac- 
cording to this theory, potassium hydroxide was conceived 
to be not a compound of the oxide and water but rather 
a derivative of water in which one atom of hydrogen 
was substituted by potassium. This was called the water 
type. Gerhardt recognized three types — water, hydro- 
chloric acid, and ammonia — and endeavored to classify 
all compounds under one or the other of these types. 
Gradually it was seen that other types were needed 
and the derivation from types became more and more 
compUcated. 

Berzehus, now an old man, contended for his dual- 



130 HISTORY OF CHEMISTRY 

istic theory and could not be reconciled to the change 
to the types and to the unitary theory. But the great 
master was engaged in a vain struggle. In the course 
of the discussion he formulated a new theory as giving 
a better explanation of the substitution phenomena and 
as being more in consonance with his duaHstic theory. 
This was known as the theory of conjugated compounds 
and associated with it was the theory of copulas. The 
ideas, however, were not very clear and exerted Uttle in- 
fluence upon the science. 

The discovery of the amines in 1848, the year after the 
death of Berzehus, did much to strengthen the t^^De 
theory. This was followed shortly by the important 
work of WiUiamson on the ethers, alcohols, esters, and 
acids, which he showed belonged to the water type. 
It should be noted that these types were drawn from in- 
organic compoimds, thus building upon that which was 
already fairly well known. The two great divisions of 
chemistry have proved mutually helpful in their de- 
velopment and must always be regarded as parts of one 
harmonious whole. Throughout, the question of chemical 
constitution has been the important one. 

Homologous Series. — This was a period of classifica- 
tion — one of striving after a systematic arrangement 
of the elements in inorganic chemistry and the radicals 
in organic. Pettenkofer, hoping for an all-embracing 
system, compared the elements with the compound radi- 
cals and suggested that they might be looked at from the 
same standpoint. The analogies between the radicals 
themselves had been noted and Schiel suggested that 
they might be arranged in series which would bring out 
this homology. The suggestion was adopted by Dumas 



FURTHER THEORIES AS TO STRUCTURE 131 

with regard to the fatty acids and the idea was further 
extended by Gerhardt. Diunas transferred the idea to 
inorganic chemistry and tried to arrange the elements in 
homologous series, but the analogies were too incomplete 
for success. As the knowledge of the organic radicals 
grew and the fullness of their agreement was recognized, 
homologous series became a necessary fixture in organic 
chemistry. 

Application of the Valence Theory. — It was at this time 
that the valence theory took its rise from the study of 
the organo-metaUic bodies. With its introduction struc- 
tural organic chemistry had a secure foundation. Its 
foimder was Kekule, who was born about a year after 
Wohler's noted synthesis of urea. In 1858, while pro- 
fessor at Ghent, he showed by a study of the simpler 
compounds of carbon that its valence was four. Later 
he became professor at Bonn, dying there in 1896. 

Taking his arrangement of the halogen compoimds of 
methane, it will be seen how he applied valence to the 
type theory of which he was a strong supporter. The 
series runs: CH4, CH3CI, CH2CI2, CHCI3, CCI4. The 
quadrivalence of carbon remains, while the valence of the 
radicals CH3, CH2, etc., increases by one with each hydro- 
gen lost. But his most original idea was in regard to com- 
pound radicals containing more than one carbon atom. 
His conclusion here was that the carbon atoms were 
directly connected with each other. Thus the ethyl radi- 
cal would be CH3-CH3; the propyl CHs-CHs-CHg, 
the hydrogens being joined to the carbons and the latter 
forming an open chain. Kekule's desire in constructing 
these formulas was not merely to show how the atoms 
were united but to give a picture of the way in which re- 



132 HISTORY OF CHEMISTRY 

actions took place. So these formulas were called 
rational. He regarded as the most rational the one 
which at the same time expressed the greatest nimiber 
of metamorphoses. 

The writing of the first graphic formulas was attempted 
by Couper, also in 18o8, He insisted, however, upon 
halving the atomic weight of oxygen and this necessitated 
writing two atoms of oxygen where modern formulas 
would show only one. This was a disadvantage in the 
matter of making a favorable impression and receiving 
recognition. In 1861 Kekule published the first volume 
of his epoch-making text-book which presented fully to 
the pubhc his views upon structural organic chemistry, 
illustrated by a very large nimiber of examples. Kekule 
also gave as his explanation of the differences between 
the two great divisions of organic substances the open 
chain and closed chain formulas, thus satisfactorily clear- 
ing up many difficulties and paving the way for the re- 
markable development of organic chemistry which fol- 
lowed in the next decades. These two divisions were 
called, respectively, the fatty (later aUphatic) and the 
aromatic (cycUc) series. In the former methane and its 
homologues were the dominant radicals; in the latter, 
benzene. 

The Benzene Theory. — The so-called aromatic group 
or series of substances showed usually a higher ratio of 
carbon to hydrogen than did the ahphatic. Where the 
ratio was the same or approximately the same the stabil- 
ity and capacity to form compounds were much greater 
in the aromatic group. Thus diproparg^d and benzene 
both have the formula CeHe, but the former is quite 
unstable while the latter stands the action of the strongest 



FURTHER THEORIES AS TO STRUCTURE 133 

acids. Manifestly the difference could only be accounted 
for by assuming a different arrangement of the atoms. 
But to find an arrangement which would account for 
such unusual stabihty was a perplexing problem. It is 
best to give in Kekule^s own words the account of how 
he reached a solution, bearing in mind that the case 
cited above was not the only one; nor was it the special 
one with which he was concerned. 

^^I was busy writing on my text-book but could make no 
progress — my mind was on other things. I turned my 
chair to the fire and sank into a doze. Again the atoms 
were before my eyes. Little groups kept modestly in the 
background. My mind's eye, trained by the observation 
of similar forms, could now distinguish more complex 
structures of various kinds. Long chains here and there 
more firmly joined; all winding and turning with a snake- 
like motion. Suddenly one of the serpents caught its 
own tail and the ring thus formed whirled exasperat- 
ingly before my eyes. I woke as by hghtning and spent 
the rest of the night working out the logical consequences 
of the hypothesis. If we learn to dream we shall perhaps 
discover truth. But let us beware of publishing our 
dreams until they have been tested by the waking 
consciousness.'' 

This was the origin of the benzene ring, an assumption 
which expanded through the labors of many workers 
into the accepted theory of the present and the basis 
of many of the most remarkable and important acliieve- 
ments of creative chemistry. 

Stereochemistry. — One manifest lack in these struc- 
tural formulas, if they were intended to give a complete 
picture of the molecule, is that they are written on plane 



134 HISTORY OF CHEMISTRY 

surfaces and hence confined to space of two dimensions, 
whereas they must of necessity occupy space of three di- 
mensions. A perspective representation is also necessary. 
It was Van't Hoff who, in 1874, while still a student, fas- 
tened attention upon this and laid down the governing 
principles a httle later in his book Chemistry of Space. 
This branch of chemistry is known as stereochemistry. 
Necessarily perplexities and difficulties increase if 
chemists are restricted to a knowledge of chemical 
reactions as the sole means of determining these space 
relations. An observation made by Laue in 1913, his 
subsequent work, and that of the Braggs, father and son, 
have introduced a new method, at least for crystaUine 
structure, in the X-ray spectra. And already much 
progress has been made both for organic and inorganic 
molecules and the outlook is most promising for further 
revelations. By this method the molecules are actually 
photographed and can be studied in all the accuracy of 
detail and perspective. Success turns on the correctness 
of interpretation of the results. 

Pasteur (1822-1895). — One of the greatest of scien- 
tific men, as well as one of the greatest benefactors of 
his race, was Louis Pasteur. Born of a peasant family 
in a small French village he revolutionized the science 
of medicine when he introduced and proved his germ 
theory of disease. He also accomplished much for the 
wine and other industries of his native land. 

His most important contributions to chemistry came 
through his investigation of the tartaric acids and in 
general the phenomena of physical isomerism. There 
are four of these acids having the same formula. Their 
separate existence can not be accounted for by the usual 



FURTHER THEORIES AS TO STRUCTURE 135 

method of possible changes in the arrangement of the 
atoms, yet they do exist and exhibit certain physical dif- 
ferences. One of these extra forms had been known 
for a long time as racemic acid. It is often found in grapes 
along with tartaric acid and sometimes has substituted 
to a considerable extent the normal tartaric acid in the 
juice. Its acid potassium salt is more soluble than that 
of tartaric acid and hence does not separate out well 
in the aging of wine and renders the wine of inferior quahty. 
Pasteur noticed that the sodiimi ammonium salt de- 
posited two kinds of crystals. These crystals showed 
hemihedral faces so related that one crystal corresponded 
to the image in the mirror of the other. He found further 
that the acid from one variety of crystals was dextro- 
rotary while that from the other was laevo-rotary. 
This is referable immediately to space arrangement, 
as was represented in the mirror image. As he published 
an account of his work in 1848, it marks the beginning 
from which stereochemistry was later developed. Pre- 
vious observers, notably Biot, had remarked a connection 
between optical rotation and hemihedral forms in such 
crystals as quartz, and it had been shown that the geo- 
metrical form determined the direction of the rotation. 
When one recalls that Pasteur's observations were made 
with solutions in the tube of the polariscope and also 
that later it was found that this property was also ex- 
hibited in the gases of certain volatile organic substances 
it becomes possible to trace the phenomenon directly 
back to the molecule. The construction of the molecule 
also evidently determined the crystal form. Considering 
such facts as these, Pasteur reached the conclusion that 
the molecule itself was unsymmetrical. It is now known 



136 HISTORY OF CHEMISTRY 

that tartaric acid contains two unsymmetrically arranged 
carbon atoms. In the undeveloped state of organic chem- 
istry at that time Pasteur was unable to refer the lack 
of symmetry to any definite atoms. 

His study of fermentations and brilliant work in trac- 
ing these changes to the hfe processes of micro-organisms 
have transformed the outlook of more sciences than one 
and wrought miracles for human comfort, health, and 
happiness. His name will be associated always with 
the conquering and control of contagious diseases. 

Syntheses from Coal Tar. — The foundations for the 
important coal tar industries, especially relating to dye 
stuffs, were laid by Hofmann (1818-1892) and the first 
artificial or synthetic color was made in 1856 by Perkin, 
one of his students. Hofmann was at that time a pro- 
fessor in the Royal College of Chemistry in London. 
At the time of his death he was a professor in the Univer- 
sity of BerHn. 

Tar is recovered as a by-product in the distillation of 
coal and until the middle of the nineteenth century Uttle 
use had been found for it beyond its use as fuel. In 1843 
Hofmann foimd that it contained aniline and this led 
to his valuable researches upon the amines. In 1845 
he foimd that it also contained benzene and the synthetic 
production of anifine in large quantities from this source 
followed. In 1856, in the course of his investigation of 
the action of oxidizing agents upon crude aniUne oil, 
Perkin discovered the dye known as mauve. This was 
the first of the coal tar colors. Griess, another assistant 
of Hofmann, studied the diazo compounds and the manu- 
facture of the azo compounds and dyes was founded 
upon the results of his researches. In 1868 Graebe and 



FURTHER THEORIES AS TO STRUCTURE 137 

Liebermann prepared alizarin, the red coloring matter 
of madder, from anthracene. After some years of costly 
and toilsome work at a later period Baeyer, who had 
studied imder Bimsen and was then a professor at Munich, 
worked out the synthesis of indigo from naphthalene. 
These discoveries mark the triumphant progress of a 
great industry which soon branched out from the arti- 
ficial reproduction of natural coloring matters into an 
almost unlimited field of creation of brilliant colors un- 
known before. Here the constitution of the molecules 
was painstakingly worked out and the chromophoric 
groups of atoms identified. 

Further, plant perfumes were synthesized and new ones 
prepared. So, too, with the remedial agents. New 
organic preparations were studied as to their physiological 
properties and action and the field of synthetic medicines 
opened up. This required cooperation between the chemist 
and the physiologist and many skilled workers entered 
this field. New and terrible explosives were discovered 
and then others sought for among these organic com- 
pounds; and in these later years the deadly poison gases 
were manufactured for use in warfare. For good or ill, 
chemistry as a creative art came into its own. The 
modern world has become dependent upon chemical re- 
search and the knowledge and skill of the technical 
chemist. 



CHAPTER XV 
PHYSICAL CHEMISTRY 

While in one sense physics and chemistry are distinct 
branches of science, both are concerned with the same 
great natxn'al laws. The atom and the electron belong 
to both and now that matter in its ultimate analysis 
has been identified with energy there is scarcely a dividing 
line between them. In the earher stages of their develop- 
ment one might be both physicist and chemist and often 
was. The great accumulation of facts and theories has 
rendered it practically impossible to be master in both. 
Where the two sciences merge into one another, however, 
a new branch has grown up and this is called physical 
chemistry. Its growth has been rapid and its importance, 
both in piu*e and appUed science, can scarcely be over- 
estimated. 

Physical chemistry may be said to have had its beginning 
in the teachings of Berthollet in his Essai de statique 
chimique pubhshed in 1801. He brought to Hght the fact 
that a chemical reaction depended upon the masses, or, 
as it would be expressed now, the concentration of the 
reacting substances; and that solubiHty, volatiUty, and 
such physical properties of the products influence materi- 
ally the course of the reactions. Under certain conditions 
equiUbria were reached. The importance of these ob- 
servations was not realized at that early date. Chemists 
were busied with what they regarded as more important 

138 



PHYSICAL CHEMISTRY 139 

work — the discovery and accumulation of facts and the 
testing of the more obvious fundamental laws. 

Such investigators as Gay-Lussac with his gas laws, 
Avogadro and Ampere with their basis of the kinetic 
theory, Dulong and Regnault with their researches upon 
specific heat and the laws controlhng its action, were most 
prominent among the early builders in this middle ground 
between the sciences. A still greater influence was exerted 
by Bunsen some fifty years later. In cooperation with 
Kirchoff he constructed the spectroscope which has con- 
tributed so much to the knowledge of nature and its 
changes both on the earth and in the extra-terrestrial 
bodies. By means of this instrument Kirchoff showed 
that radiations are absorbed by the vapors of the sub- 
stances which emit them, and so revealed the meaning 
of the dark fines which had been found in the solar spectra. 
Other absorption spectra are given by solutions the exact 
physical explanation of which is still an unsolved problem. 
Bunsen's photochemical investigations taught that the 
degree of change brought about by fight was proportional 
to the intensity of the fight and the time of exposure, 
and that the fight absorbed in a reacting medium 
was proportional to the change produced. His '^ photo- 
chemical induction^' is yet without satisfactory expla- 
nation. Still it was of first importance to learn that 
photochemical absorption followed the usual laws. The 
invention of the polariscope and the study of polarization 
phenomena, the progress of hydrolysis, etc., aided greatly 
in the development of physical chemistry. 

Law of Mass Action. — As has been pointed out, the 
basis for this was laid by Berthollet, but its bearing 
was not realized and the observations were practically 



140 HISTORY OF CHEMISTRY 

forgotten. After half a century had elapsed the details 
were gradually worked out. Thus Wilhelmy, in his in- 
vestigations upon the inversion of sugars by acids, studied 
the hydrolysis of sugars by means of acids under con- 
ditions in which temperature, acids, etc., were varied. 
From these observations he deduced a mathematical ex- 
pression for the velocity of the reaction. A Uttle later 
Berthelot examined the hydrolysis of the esters. Guldberg 
and Waage, after more extended investigation, summarized 
the results and proposed as a law which would cover the 
known facts that when an equilibrium has been reached 
the velocity of a reaction is determined by the product 
of the active amounts of the interacting substances. 
To account for the relationships obtaining in hetero- 
geneous equilibria the phase rule has been adopted. 
The essential principles involved in this were worked out 
by Willard Gibbs, whose work was pubHshed in 1876. 
This rule is now a matter of everyday appUcation in work 
which would otherwise prove very baffUng. 

Electrolsrtic Dissociation. — With the announcement by 
Arrhenius in 1887 of his theory of electrolytic dissociation 
the importance of physical chemistry and its intimate 
bearing upon the ordinary reactions and phenomena of 
the laboratory began to be recognized and the attention 
of chemists generally was attracted to it. Much work had 
been done previously on electrolytic association but at 
various times and in a disconnected way. Arrhenius 
gathered these facts in addition to his own observations, 
showing the connection between them and the important 
conclusions to which they led. Faraday had found that 
in the decomposition of an electrolyte by an electric 
current definite amounts of the products are obtained at 



PHYSICAL CHEMISTRY 141 

the electrodes on the expenditure of a given quantity 
of electricity and these amounts are in equivalent weight 
proportions. The intensity of the current necessary for 
the dissociation was determined, in his opinion, by the 
strength of the attraction holding the molecules together. 
He concluded that the atoms or radicals composing the 
electrolyte acted as the carriers of the current and called 
them ions, naming the positive electrode anode and the 
negative cathode, and the ions anions and cations, re- 
spectively. At first the assumption was that the anion 
and the cation migrated with equal velocities. Hittorf 
showed that this was not the case. Wilhamson introduced 
the idea that a molecule was not a rigid structure always 
made up of the same identical atoms but was capable 
of exchanging with corresponding atoms of neighboring 
molecules. Thus an ion did not pass directly from one 
electrode to the other but migrated from one molecule 
to the next, effecting the necessary interchange. Clausius 
adopted this idea of exchange and brought additional 
facts to its support. Later Kohlrausch carried out many 
experiments upon the conductivity of solutions and con- 
firmed the work of Hittorf. His conclusion was that each 
ion, regardless of the electrolyte of which it was a com- 
ponent, had a definite migration velocity which might 
be measured by its relation to some standard. 

Physical Properties of Solutions. — The problem of 
what takes place in solutions was next attacked from a 
different point of view. It had been known for a long time 
that the freezing point of a hquid is lowered by dissolving 
various substances in it; also the vapor pressure is lowered 
or, as ordinarily expressed, the boihng point is raised when 
the hquid contains substances in solution. No regularity 



142 HISTORY OF CHEMISTRY 

had been observed, however, nor law deduced. The only 
observation bearing on this is that of Blayden, who worked 
in the laboratory of Cavendish. He studied the influence 
of various dissolved substances upon the lowering of the 
freezing point and found that when he compared solutions 
of the same compound the degree of lowering was pro- 
portional to the amount of substance dissolved. 

In 1881 Raoult took up the investigation of this lowering 
of the freezing point and showed by his experiments that 
when different substances were used with the same sol- 
vent the lowering of the freezing point in each solution 
was inversely proportional to the molecular weight of 
the substance dissolved. Hence if the quantities taken 
were proportional to the molecular weights the degree of 
lowering would be the same. Turning then to the in- 
fluence of such dissolved substances upon the boihng point 
he found an analogous influence upon the raising of the 
boiling point. In the hands of other investigators it was 
soon found that the matter was not so easily solved. 
There were many irregularities and exceptions which 
demanded explanation. The statement that behavior 
in solutions was independent of the nature of the solvent 
and of the dissolved substances could not be generally 
apphed and was not true in that form. The difficulties 
were removed and the explanation made clear by experi- 
ments carried out along an apparently different line. 

Osmotic Pressure. — More than one hundred years 
earher NoUet had observed that when water and alcohol 
are separated by a membrane the water passes through 
the membrane into the vessel containing the alcohol 
and at the same time exerts a considerable pressure upon 
it. In 1877 Pfeffer measured this pressure, which is ex- 



PHYSICAL CHEMISTRY 143 

hibited also between water and an aqueous solution or 
between different solutions, and de Vries showed that 
solutions could be prepared which exhibited no pressure 
when thus separated. 

Experiments of Van't Hoff . — The connection between 
osmotic pressure and the facts discovered as to boiling 
and freezing points and vapor pressure was worked out 
in the latter part of the nineteenth century by Van't 
Hoff, who also made a thorough investigation of the phe- 
nomena of osmotic pressure. He found in the course 
of the latter investigation that when a substance is dis- 
solved in a Uquid the molecules exert the same sort of 
pressure on its surface as they would if they existed in 
the form of a gas and occupied the same volume. The 
bearing of the molecular weight relations then is evident. 
When substances are taken in the proportion of their 
molecular weights they contain the same number of mole- 
cules and will obey the gas laws as to pressure, etc., 
provided there is a freedom of movement similar to that 
in a gas and no change in the molecule. 

Ionization Theory. — Further light on the subject came 
through the work of Arrhenius on electrolysis. He 
reached the conclusion that in a solution through which 
a current is passing only a portion of the particles take 
part in the conduction. The proportion of such con- 
ducting particles he called the ^^activity coefficient." 
This activity coefficient was found to be proportional to 
the ^ ^affinity coefficient" of Ostwald. From a comparison 
of these facts of electrolysis with the facts above men- 
tioned the modern theory of ionization was reached. The 
various compounds are divided into two classes: those 
which conduct electricity, or electrolytes, and those which 



144 HISTORY OF CHEMISTRY 

do not, or non-electrolytes. The electrolytes vary in 
their conducting power. When electrolytes are dissolved 
in water they separate or ionize into two ions, one posi- 
tively and the other negatively charged. In the case 
of complete ionization there would, therefore, be twice 
as many particles present as there were molecules origi- 
nally. This is approximately the case when strong acids 
or bases are the electrolytes. Twice the pressure would, 
therefore, be exerted, as this is due to the number of the 
particles and is independent of their nature. Those 
which do not electrolyze show no change in the number 
of particles and hence behave normally. The strong 
support of the ionization theory by Ostwald did much 
to bring about its general introduction. It has served 
to explain many reactions which were before difficult 
to understand, though there are still instances which pre- 
sent difficulties in the way of its application. 

Colloidal Chemistry. — The conceptions introduced by 
physical chemistry now play an important part in all 
branches of chemistry and are essential to the under- 
standing of much that goes on both in experimental 
and technical work. Among other things it has been 
made clear that besides the well-known molecular com- 
pounds with definite constitution and structure there are 
other molecular aggregations, often containing hundreds 
of atoms, which do not follow the fundamental laws of 
chemistry, as, for instance, the law of definite propor- 
tions, and which play a most important part in every- 
day life and in the industries. These are grouped as col- 
loids and form a distinct division of the science under 
the name of colloidal chemistry. The first work upon 
these substances began with Graham's diffusion experi- 



PHYSICAL CHEMISTRY 145 

ments in 1850 in which he found that by means of dialysis 
substances could be separated into crystalloids, which 
form real solutions and diffuse more or less readily through 
an animal membrane, and colloids, which do not diffuse 
at all or only very slowly. Some colloids are apparently 
soluble in water, but it has been proved that they are really 
present in a state of very fine subdivision and are only 
suspended in the Hquid. A very large number of sub- 
stances have this property of existing as colloids, whether 
elements or compounds, and a new field of very interesting 
and complex phenomena has been opened up. Colloids 
form what are called adsorption compounds which are 
more or less stable to the action of water. In these 
the components may be present in indefinite proportions. 



CHAPTER XVI 
BIOCHEMISTRY 

As has been related, the old man-erected barrier of a 
hypothetical vital force was overthrown and organic 
chemistry developed into that branch of the science 
which embraced the largest number of known compounds, 
running up into the hundreds of thousands, and attracted 
most of the investigators. It was reaUzed that hfe proc- 
esses, as they are still called, are identified with physical 
and chemical changes which obey the ordinary laws 
of those sciences and can be relied upon to bring about 
the usual results. These changes are definitely subject 
to the influence of the various forms of energy and take 
place normally at a normal temperature and under a 
normal pressure. Under changed temperature or pressure 
they take an abnormal direction or velocity. Many of 
the reactions belong to the reversible class. They also 
obey the mass law and are affected by changes of con- 
centration. Until these facts were duly recognized the 
art of medicine was chiefly on an empirical basis and could 
not be called a science. 

The complexity of the molecules involved, many being 
colloidal in nature, and the diversity of the possible 
changes render this the most difficult of the sciences 
to master, requiring as it does an expert knowledge of 
physics, chemistry, and physical chemistry, besides other 
sciences. Just what constitutes life remains unknown. 

146 



BIOCHEMISTRY 147 

There is no spontaneous generation or autogenesis, and 
life processes which have once come to a definite end 
cannot be started again, though some of the minor re- 
actions have been caused to repeat themselves under 
artificial conditions. So there is in a way a hfe barrier 
after all, but not one which forbids the reproduction 
of substances formed in plants and animals and which 
nulUfies the laws and conceptions of the sciences. The 
field is open for intelhgent study and in biochemistry the 
chemist finds the culmination of his science. 

The study of the constituents of plants and animals 
and especially of the chemical changes taking place 
among them, forms the branch known as biochemistry. 
This is a far cry from the ancillary position occupied 
by the science in its earher periods. The term physio- 
logical chemistry covers in part the same field but has 
a more limited significance in so far as chemistry is con- 
cerned. Of course the examination of the constituents 
of organic nature did not escape the attention of those 
early chemists who laid the foundations of modern chem° 
istry. Fourcroy, Vauquelin, Chevreul, Berzelius, and 
others contributed investigations along these lines. 
After learning the composition of organs, secretions, etc., 
to which knowledge many chemists contributed, the 
next step was to find out the conditions under which these 
substances were formed, their relation to one another, 
and the changes they underwent — in other words, the 
reactions going on in the body. This has proved a far 
more difficult task. A vast amount of work remains to 
be done along these lines. Still chemical investigation 
has rendered great service in clearing up much that was 
obscure and in disproving mistaken conceptions and 



148 HISTORY OF CHEMISTRY 

misleading hypotheses. The number of these investiga- 
tions is far too great to be detailed here, or in most cases 
even mentioned. There was the early work of Mulder 
and Liebig and others on the proteins, followed many 
years afterwards by the epoch-making researches of Emil 
Fischer in which he studied their hydrolysis and showed 
certain of them to be made up of amino-acids, synthesized 
them, and revealed the products of their hydrolysis. 
The proteins play a leading part in the life processes 
and a knowledge of them is of the utmost importance. 
They still form probably the chief point of attack on 
the part of chemists. The almost endless variety of 
these substances tells us that we are yet far from fully 
understanding their composition and functions. 

Through the investigations of Chevreul and those 
who followed him the composition of the fats and their 
hydrolytic products are known. Emil Fischer has given 
a deep insight into the constitution of the sugars. Starch 
and other carbohydrates and the results of their hydrol- 
ysis have been studied. The Schmidts, Hoppe-Seyler, 
Nencki, and Ludwig have revealed much as to the blood, 
its composition and coagulation, and the gases carried. 
The differences between venous and arterial blood have 
been much discussed and, in fact, satisfactorily solved. 
The researches upon inhaled and exhaled air and the 
processes taking place in the lungs are far too numerous 
to recount; and so also with regard to the metaboKsm 
of foods. The distinction drawn by Buchner in 1896 
between fermentation changes caused by micro-organ- 
isms and those caused by enzymes — hydrolytic changes 
brought about by the cell itseK or by a substance secreted 
by the cell but acting apart from it — was of import, 



BIOCHEMISTRY 149 

though intracellular action must be taken into consid- 
eration and the mechanism of the changes is not yet 
definitely understood. 

Of the many other contributors to the development of 
biochemistry mention may be made of Abderhalden, 
Atwater, Lusk, Chittenden, Hammarsten, and Van 
Slyke. The field is too large to dg more. 



CHAPTER XVII 
RADIOACTIVITY 

The Discovery. — The story of radioactivity, this 
latest and crowning marvel in scientific discovery, really 
begins with the phenomena in the tubes which were 
constructed by Crookes in 1879 and which have been 
named after him. The phenomena observed in these 
high-vacuum tubes when a current of high potential was 
passed through them led Crookes to suggest that one 
might be deaUng with a fourth state of matter, which was 
not a bad guess when one considers the revelations which 
have followed. There were observed streams of minute 
particles which could be deflected by a magnet and so 
had some of the properties of matter. These proceeded 
in straight streams through perforations in the anti- 
cathode. There were also contrary streams of negative 
electrons, and later Rontgen found that by use of the 
anti-cathode very penetrating rays were obtained. These 
were after the order of hght and easily passed through 
the glass walls of the tubes. They affected sensitive 
plates and photographs could be taken with them. He 
called these X-rays. 

As these phenomena were accompanied by phospho- 
rescence, Becquerel conceived the idea that similar photo- 
graphs might be taken by means of naturally occurring 
phosphorescent substances, a number of which were 
known. His efforts failed with all phosphorescent sub- 

150 



RADIOACTIVITY 151 

stances known to him until he tried the salts of uranium 
with which he had previously done some experimental 
work and some of which he had noticed were phospho- 
rescent. One class of these salts is phosphorescent, 
while the other is not, but he found that both classes 
gave off rays that acted upon the sensitive plates. These 
new unknown rays for a time, therefore, were known as 
Becquerel rays. Further investigation showed that all 
minerals containing uranium showed this effect. Ex- 
amination proved that the intensity of the activity of an 
uranium compound was determined solely by the amount 
of uranium and was independent of the other elements 
present with which it might be combined. It was accord- 
ingly a property of the uranium atom and to be classed 
as a new atomic property. Others were attracted to 
this search and it was found that only one other element 
possessed this property in any marked degree and that 
was thorium. Rubidium and potassium showed very 
slight and partial activity. 

Radium. — During an examination of other uranium 
minerals in which the intensity of the radiations was 
measured Madame Curie discovered that certain of them 
showed a much greater activity than could be ascribed 
to the amount of lu-anium present. From this she con- 
cluded that they must contain some unknown element 
or elements which were more radioactive. Working 
with very large quantities of material and in a most 
painstaking and laborious manner, she found that 
by using ordinary laboratory methods, such as precipi- 
tation and crystallization, she obtained a minute residue 
which was intensely radioactive. One such residue was 
obtained when bismuth salts were used as the reagent. 



152 HISTORY OF CHEMISTRY 

This gave spectroscopic indications of the presence of 
a new element which she named poloniimi but which 
she was imable to isolate completely. When barimn salts 
were used as the precipitating reagent she obtained 
another residue, also exceedingly active. From this 
the active element was separated, its spectrum mapped, 
and its atomic weight, valence, and other properties 
determined. To this she gave the name radium. Two 
other elements have been detected by analogous pro- 
cesses — actinium by Debierne and ionium by Boltwood 
— but their separation in a pure state has not been 
accomplished. 

The Radiations. — When the emanations coming from 
these radioactive substances were examined by the ioni- 
zation method they were found to be electrically charged. 
By means of the electroscope some were found to carry 
a positive and some a negative charge. Their power 
of penetration, as tested by thin sheets of metal, etc., 
differed greatly, and their velocity ranged from one-fif- 
teenth that of light to one many times greater. Also, 
by examination in a magnetic field it was found that 
some were not deflected, some slightly, and some very 
greatly. It was evident that the radiations were com- 
posite and made up of different kinds of rays. Comparing 
the results noted above, three classes of rays were dis- 
tinguished and identified. One that was called the alpha 
ray was positively charged, was sUghtly deflected, and had 
a low penetration but the greatest power of ionization. 
It had the least velocity, about one-fifteenth that of 
light, and produced scintillations upon a zinc sulphide 
screen. This was identified with the canal rays which 
had been observed in the Crookes tubes. A second, 



RADIOACTIVITY 153 

the beta ray, was negatively charged and greatly de- 
flected. It had an ionizing power of only one per cent 
of that of the alpha ray, a greater penetrating power, 
and a velocity after the order of hght. This was identi- 
fied with the negative electron. The third variety of 
ray was identified with the X-ray. It was not charged 
electrically nor deflected by the magnet, had only the 
hundredth of a per cent of the ionizing power of the alpha 
ray and by far the greatest penetrating power. Its 
velocity was found to be after the same order as that 
of hght. In other words, here were chemical substances — 
elements — which gave rise to the same phenomena that 
had been observed in the Crookes tube. 

Radioactive Substances. — It was soon discovered 
that radioactivity could be induced in a wire or sheet 
of metal suspended over a radioactive substance; also 
that the radioactive substance could be separated from 
a solution of a thorium or uranium compound by the 
ordinary chemical operation or precipitation. In this 
it showed its nature or behavior to be similar to that of 
the ordinary chemical element or compound. But this 
additional fact was noted. When in the solution of the 
uranium salt, for instance, the radioactive substance 
had been separated by precipitation the uranium salt 
became inactive and the activity was transferred to the 
precipitate. In the lapse of time, however, the uranium 
regained its activity and the precipitate which had been 
removed lost it. The operation could be repeated as 
often as desired. Some process was going on in which 
the uranium or thorium atoms played the part of a chem- 
ical factory producing continuously hitherto unknown sub- 
stances. But the process was either one of producing 



154 HISTORY OF CHEMISTRY 

something out of nothing or generating these products 
out of their own substance. 

A number of new substances were obtained in this 
way, were separated, examined, and found to be them- 
selves sending off radiations and undergoing changes. 
Some lasted only a very short while, others days or 
years, and there were yet others whose life period could 
only be calculated in terms of centuries after measuring 
the rate of decay. These new substances were distin- 
guished from one another chiefly by their duration 
value and by the character of their emanations. At least 
three of these are gases and these gases are monatomic 
and belong to the argon group in the Periodic System. 
For some the spectra were mapped and chemical prop- 
erties, valence, and other distinguishing characteristics 
determined. They were distinct elements with the 
usual elemental physical and chemical characteristics. 
Altogether more than thirty of these strange new ele- 
ments have been discovered and three distinct equi- 
librium series determined. 

Disintegration Theory. — Rutherford proposed as an 
explanation of these transformations a theory of dis- 
integration which has been generally accepted. While 
there have been many workers in the field who have 
rendered valuable service, it is to this distinguished 
man, who combined the attainments of mathematician, 
physicist, and chemist along with rare insight and vision, 
that science is chiefly indebted for the elucidation of 
the phenomena of radioactivity and the resulting clear- 
ing up of many of the unsolved problems of the past. 

According to this theory, one out of a vast nimiber 
of uraniimi atoms becomes unstable in every minute 



RADIOACTIVITY 155 

fraction of time and bursts with great violence for so 
tiny an object, expelling one or two alpha particles and 
forming a new atom. This is much more unstable and 
breaks up after a shorter interval, losing an electron; 
and so there is a series of transformations in which alpha 
particles and electrons are expelled and the great energy 
transformed, it may be, into the ganama or X-rays. 
In this series we come to radium, more stable, it is true, 
but also disintegrating. Finally an end-product seems 
to be reached and in this the change is at least exceed- 
ingly slow, though it is still radioactive. This end- 
element is so similar or closely akin to lead that it can 
not be separated from it and is called radioactive lead. 
Its atomic weight has been most carefully determined 
by Richards, Honigschmid, and others and the atomic 
weight found to be over one-half a per cent less than 
that of ordinary lead. In the same way the thorium 
atom breaks up and there is formed a different series 
in which the rate of disintegration is different. The 
end-product again is a radioactive lead, and this time 
the atomic weight is greater than that of lead. It has 
been noted that in uranium and thorium minerals there 
are fairly accordant ratios between the amount of the 
uranium or thorium and these end-products, indicating 
that a sort of equilibrium has been reached. 

This disintegration is entirely beyond outside control. 
No means of starting or stopping it is known. There 
would seem to be an inherent instability in these the two 
largest of the atoms. Neither the highest nor the lowest 
temperatures obtainable have any effect in increasing 
or retarding the velocity of change. Furthermore, the 
energy freed is beyond all comparison greater than that 



156 HISTORY OF CHEMISTRY 

from any other known source. This has been shown 
by calorimetric determinations. 

The rays emanating from a substance hke radiimi are 
known to exert a profound effect upon various organic 
and inorganic substances, the molecules of compounds 
and elements undergoing dissociation, and proof has 
been brought forward that at least one atom — that of 
nitrogen — has been decomposed when subjected to the 
action of the alpha particles. That the atom of one ele- 
ment can be built up by these rays has been clearly shown 
by a remarkable experiment of Rutherford. In this ex- 
periment alpha particles coming from radium emanations 
passed through thin glass walls of a tube into a surround- 
ing tube with thicker walls through which they could 
not pass. This outer tube had been carefully evacuated, 
so far as possible, of all gas before the beginning of the 
experiment. A sufficient amount of the alpha particles 
had entered it in the course of two days to yield a dis- 
tinct spectrum which coincided fully with the spec- 
trum of hehimi. The hehum atom, therefore, is built 
up of alpha particles and electrons obtained from the 
glass or during the sparking necessary to get the arc 
spectrum. 

Constitution of the Atom. — Basing his conception on 
this experiment and on the disintegration phenomena, 
Rutherford announced his theory as to the constitu- 
tion of the atom. In this the atom is conceived to have 
a nucleus of positive electricity surrounded by one of 
negative electricity or, to express it a little differently, 
to be made up of a positive nucleus of protons and 
electrons with outer envelopes of electrons moving in 
orbits. This theory received confirmation from the facts 



RADIOACTIVITY 157 

discovered in connection with the " recoil atoms '^ and 
the " stopping power '' exhibited by various metals and 
gases. Rutherford's atom was supposed to be spherical. 
Cubical atomic models have also been suggested. Bohr's 
model and that of Langmuir differ from that of Ruther- 
f o'rd in details but all agree as to the atom being composed 
of negative and positive electricity. It is interesting to 
note that after the lapse of a century there is a return 
to the suggestion of Davy and the more elaborated con- 
ception of BerzeUus. Changed in form and detail and am- 
plified through greatly increased knowledge, the conception 
comes back with a firm basis of experimental evidence. 

The New Atom and its Properties. — It would seem 
that at last there was at hand an explanation of such 
imsolved problems as the combining power and the 
valence of the atom and the underlying principle of the 
Periodic System. Soddy and others have done much 
to bring the new facts to bear upon such problems as 
these. Entire agreement has not been reached but some 
results can be given without going into details. 

In the first place, it was found that the loss of an alpha 
particle reduced the atomic weight of one of these new 
elements by four, which is the atomic weight of helium. 
At the same time the atom in its chemical relations 
changed two groups from the negative to the positive 
side in the Periodic Table. The loss of a beta particle, 
or electron, caused a change of one place in the opposite 
direction, involving a change in valence and combining 
power or afiinity. The loss of two electrons neutralized 
the loss of one alpha particle. Noting that three alpha 
particles are lost from uranium to radium, the atomic 
weight of radium should be 238 - 12 = 226, which 



158 HISTORY OF CHEMISTRY 

agrees with the actual determinations. So, too, the 
atomic weight of the radioactive lead has been calculated 
with strong confirmatory experimental evidence from 
actual determinations. 

In ionization there is an exchange of electrons between 
the separating ions. When a current is passed through 
a solution of an electroljrte these ions, on reaching the 
electrodes, regain or give up the electron, respectively, 
and ordinary atoms result. Again, the properties of 
the atoms are not dependent upon nor determined by 
the atomic weights, which had practically been recognized 
by Mendeleeff in constructing his table, though he laid 
down as a fundamental principle that the properties 
were functions of the atomic weights. The mass or 
weight is just one of the properties and is itseM deter- 
mined by the positive nucleus. The properties are deter- 
mined by the electrical relations and valence is changed 
by the loss of an electron. For instance, when the valence 
of iron or copper is changed the atom is definitely trans- 
ferred to another group, a process which can readily be 
reversed. 

So a new conception arises, namely, that in the build- 
ing up of these elements there is a definite order and 
that in the series each has an assigned place correspond- 
ing to a number which is now called the atomic number. 
This nmnber can be determined by the '^stopping power'' 
of the element in question, that is, its relative penetra- 
bility. The atomic number is now determined more con- 
veniently and accurately by the method of Moseley in 
which the shifting of certain fines in the X-ray spectra of 
the elements is mapped and their order definitely settled. 

Factors in Element Fonnation. — It is manifest that 



RADIOACTIVITY 159 

given certain factors of balanced electrical relations it 
would not be difficult to construct a series such as that 
which is found in the known elements presenting numer- 
ical regularities as to their atomic weights. It was this 
that Cooke and Dumas attempted to do in the middle 
of the nineteenth century, though they were of course 
in ignorance as to the bearing that electricity might have 
in the matter. A number of chemists and physicists 
of the day have been engaged in this task since the 
Rutherford atom was recognized. The work is neces- 
sarily in the tentative stage as yet. The factors usually 
taken are hehum and hydrogen, as suggested by Harkins, 
though others have been suggested. As Rutherford has 
pointed out, helium is a secondary structure and itself 
made up of four hydrogens. 

Isotopes. — In attempting to place the radioactive ele- 
ments in their proper positions in the Periodic Table 
Soddy found that when they were classified according 
to their properties and the losses of alpha particles and 
electrons sustained, several closely analogous elements 
would fall in the same space, though their atomic weights 
might be widely different. Thus there are nine isotopes 
of lead with the atomic number 82. This name isotope 
was suggested by Soddy to designate an element which 
is so closely analogous to one of the known elements that 
it is chemically inseparable. The difference hes in certain 
physical properties, notably the atomic weight. It has 
been suggested that certain of the rare earths which 
have presented great difficulties in the way of their 
proper placing in the Table are also isotopes. 

Another recent development in this matter of isotopes 
is that some of the well-known elements, such as neon, 



160 HISTORY OF CHEMISTRY 

chlorine, hydrogen, etc., can by physical methods, mainly 
diffusion experiments, be separated into portions which 
exhibit all of the chemical properties of the element 
but have distinctly differing atomic weights. It is prob- 
ably true then that in determining the atomic weight 
of an element the final result is an average of the weights 
of the atoms present. 

Recent methods devised by J. J. Thomson and Aston 
have made it possible to determine the number of iso- 
topes of an element, their relative proportion with an 
accuracy of 10-20 per cent, and their masses or atomic 
weights with great accuracy. These methods can be 
appHed to the determination of the atomic weights of the 
known elements and exceed in accuracy the best chemical 
determinations. By this means it has been shown that 
atomic weights are whole numbers when referred to the 
standard oxygen as sixteen. This is true up to and includ- 
ing chlorine and probably will be found true of the others. 
In the case of hydrogen the atomic weight 1.008 obtained 
by chemical methods is confirmed. 

The nucleus, therefore, is made up of alpha particles 
called protons and of electrons. According to Aston, it 
is electrically neutral. This is called the electrical con- 
tent and decides the atomic weight of the element and 
its position in the Periodic System. The surrounding 
electrons in their orbits decide the valence and the 
chemical characteristics. The term isobars has been 
adopted for such elements as have the same atomic weight 
but differ in chemical characteristics, while an isotope 
is one which has the same chemical characteristics but 
different atomic weight. 

It is suggested that the term atomic weight be used 



RADIOACTIVITY 161 

for the average weight of the element as accompanied by 
its isotopic companions and that atomic mass be used 
for the weights of the individual element and its isotopes. 

Matter and the Universe. — The impression left after 
all of this is one of instability and change constantly going 
on, not merely in the visible objects around us and in 
their components but in the very atoms themselves. 
If these, which were once called simple bodies and then 
atoms are proved to be unstable, the question of stabihty 
has merely been pushed one step farther and we reach 
the electrically charged units or the individual electric 
charges and adopt the more recent term electron. 
Mutabihty drove some of the early Greek philosophers 
to despair and an abandonment of the search. But 
man has grown in many ways into a higher being and the 
very difficulties that would thwart him are but an in- 
centive to all that is finest and highest in him. 

To show how far it is possible to peer into the invis- 
ible and the minuteness of detail to which the search 
has been pushed, it is well to close this account by citing 
certain figures given by Rutherford and confirmed by 
independent investigators as J. J. Thomson and others: 

Charge carried by the hydrogen atom, 4.65 X 10~^^ electro- 
static units. 
Charge carried by the alpha particle, 9.3 X 10~^^e.s. 
Number of atoms in 1 gram hydrogen, 6.2 X 10^. 
Mass of an atom of hydrogen, 1.6 X 10~2^ gram. 
Number of molecules per cc. any gas, 2.78 X 10^'. 



INDEX 



Abderhalden 

Acids 

Acid theory, Lavoisier's . 

Acid theory, new 

Acids, polybasic 

Activity coefficient 

Aetherin theory 

Affinity 90, 

Affinity, strength of 

Affinity tables 33, 

Affinity, views as to 

Agricola 

Air, composition of, 35, 39, 
Air, experiments on . .31, 

Albert us Magnus 

Alcohol 

AlkaHs 

Alkahs, decomposition of 

Alkalizing principle 

Amines, discovery of . . . . 
Ammonium chloride. . . . 

Ampere 

Analysis , . . 

Anaxagoras 

Anaximenes 

Apparatus 

Aqua regia 

Arabians 

Archelaus 



PAGE PAGE 

149 Arfvedson Ill 

22 Aristotle 17 

51 Arrhenius 140, 143 

104 Arsenic sulphides 5 

96 Ascending series of Glad- 

. 143 stone 84 

. 122 Aston 159, 160 

91, 92 Atmosphere 49, 57 

91, 93 Atom, composite 87 

44, 91 Atom, constitution of. . 155, 160 

43 Atom, disintegration of . . . 153 

27 Atom, nature of 81, 82, 92 

40, 46 Atoms 14, 62 

50, 61 Atoms, recoil 156 

24 Atomic attractive force ... 90 

25 Atomic chains 98 

22 Atomic models 156 

101 Atomicity 96 

105 Atomic theory ... 14, 15, 60, 126 
130 Atomic weights 65, 70, 108 

22 Atomic weights, constancy 

69 of 78 

38 Atomic weights, Dalton's 

16 rules 66 

13 Atomic weights, Dumas on 74 

18 Atomic weights, Gmelin's 

22 views 76 

19, 20 Atomic 'weights, numeri- 

13 cal relations 83 



163 



164 



INDEX 



PAGE 

Atomic weights, revision 
of 77 

Atomic weights, standard 
for 71 

Avogadro's theory 69 

Bacon, Francis 30 

Bacon, Roger 24 

Baeyer 137 

Becquerel 149 

Benzene theory 132 

Benzoic acid radical 122 

Bergman 38,92 

Berthelot 140 

BerthoUet. .42, 43, 63, 92, 103, 

138, 140 

Berzehus 73, 103, 106, 107, 108, 

110, 116, 117, 118, 120, 123, 

129, 147 

Biochemistry 146 

Black, Joseph 55 

Blayden 142 

Boerhaave 42, 91 

Bohr 89, 156 

Boltwood 151 

Boyle, Robert 30 

Bragg 134 

Bricks 6 

Bronze 4 

Buchner 148 

Bimsen Ill 

Bussy Ill 

Cannizzaro 78 

Carbon, valence of 98 

Carius 120 

Carlisle 100 



PAGE 

Cavendish 37, 112 

Cement 5 

deChancom-tois 84 

Chemistry, beginnings of. 1 

Chevreul 116, 119, 147 

Chittenden 149 

Claus .111 

Clausius 141 

Coal tar syntheses 136 

Colloidal chemistry 144 

Colors 6 

Combustion, chemistry of 34 
Combustion, Lavoisier's 

experiments 45 

Combustion, theory of . . . 36 
Combustion, views of 

Priestley 58 

Compounds 33, 38 

Compound radicals 124 

Constant proportions, law 

of 63 

Cooke 158 

Courtois 104 

Copper 3 

Copper oxides 5 

Cowper 132 

Crookes 79, 149 

Curie, Madame 150 

Dark Ages 19 

Davy .100, 105 

Davy's atoms 92 

Debierne 151 

De ViUe 77 

Disintegration theory .... 153 

Dobereiner 83, 120 

Duahsm overthrown 126 



INDEX 



165 



PAGE 

Dualistic theory 110 

Dulong 72 

Dumas ... .74, 75, 95, 121, 124, 
126, 127, 130, 158 

Dyeing 6 

Electro-chemical theory. . 121 

Electrolytes 143 

Electrolytic dissociation . . 140 

Electrimi 8 

Elements 14, 38 

Elements, additional Ill 

Elements, complex 88 

Elements, definition of . . . 52 

Elements, formation of . . . 156 

Elements, interrelated 87, 88 

Empedokles 14 

Epicurus 17 

Equivalents, electro-chem- 
ical 74 

Equivalents, Wollas ton's . 72 

Erdmann 77 

Ether 15 

Evolution of science 1 

Faraday 74, 118, 140 

Faraday's law 74 

Fa\Te 93 

Fischer, Emil 148 

Fourcroy 147 

Frankland 78, 95, 98 

Gases 28 

Gases, diffusion of 61 

Gases, mixtures of 60 

Gases, monatomic 86, 112 

Gay-Lussac 67, 103, 104, 117, 

130 
Geber 21 



PAGE 

Geoffroy 91 

Gerhardt 129, 131 

Gibbs, Willard 140 

Gladstone 84, 88 

Glass 6 

Glass apparatus 22 

Glauber 28,29,91 

Gmehn 76, 83 

Gold 2 

Gold purification 3 

Graebe 136 

Graham 95, 144 

Graphic formulas 132 

Griess 136 

Guldberg 140 

Gunpowder 25 

Hammarsten 149 

Harkins 160 

Heat, nature of 50 

Heat of reactions 93 

Herakleitos 13 

Hermes 9, 10 

Hess 93 

Hippocrates 90 

Hittorf 141 

Hofmann 120, 136 

Homologous series 130 

Hooke 36 

Hydrogen, discovery of . . . 48 

Industrial arts 2 

Industrial chemistry, 

growth of 99, 114 

Ionization theory 143 

Iron 3, 4 

Isomerism 117 



166 



INDEX 



PAGE 

Isomorphism 73 

Isotopes 80, 158, 159 

Kekul6 89, 131, 132, 133 

Kekule on valence of car- 
bon 98 

Kirchoff 139 

Klaproth 99 

Kohlrausch 141 

Kolbe 98 

Landolt 79 

Langmuir 89, 157 

Langmuir's model atom. . 156 

Laplace 93 

Laue 134 

Laurent 95, 128, 129 

Lavoisier 36, 37, 44, 93, 115, 120 

Laws 11 

Lead 3, 5 

Lead, white 5 

Leather 6 

Lennsen 83 

Liebermann 137 

Liebig 96, 118, 120, 123, 124, 
127, 148 

Lime 5 

Lockyer 113 

Ludwig 148 

Lusk 149 

Manganese dioxide 5 

Manuscripts 10, 11 

Marchand 77 

Marignac 77 

Mass action 139, 140 



PAGE 

Matter and universe 159 

Matter, nature of 32, 50 

Medicaments 7 

Mendeleeff 84 

Mercury 2 

Metallurgy 2 

Metals 2 

Metals, transmutation of, 20, 21 

Meyer, Lothar 84 

Meyer, Victor 120 

Middle Ages 24 

Mitscherhch 73 

Model atoms 156 

Monatomic gases. . .86, 113, 154 

Moore 114 

Mosander Ill 

Moseley 87 

Mordants 6 

Mulder 148 

Multiple proportions, law 

of 64 

Muriatic acid 103 

Mutabihty of nature, 11, 12, 161 
Mysticism 9 

Naming the science 8 

Nature of the atom 81, 157 

Nencki 148 

New chemistry, bases of.. 59 
New chemistry, founda- 
tions of 48 

New elements 99 

Newlands 84 

Nicholson 100 

Nitric acid 22 

Nollet 142 

Nucleus theory 129 



INDEX 



167 



PAGE 

Octaves, law of 84 

Odling 83, 95 

Organic analysis 120 

Organic chemistry, devel- 
opment of 115 

Organic substances, clas- 
sification 120 

Organic substances, La- 
voisier on 51 

Organo-metallic com- 
pounds 95 

Osmotic pressure 142 

Ostwald 143, 144 

Oxygen, discovery of 36, 56 

Paints 6 

Paracelsus 26 

Pasteur 134 

Periodic system 84 

Perkin 136 

Petit 72 

Pettenkofer 130 

Pfeffer 142 

Pharmacy 26 

Phase rule 140 

Pherekides 13 

Phlogiston 35 

Phlogiston, non-existence 

of 34 

Phlogiston theory 34 

Photo-chemical induction. 139 

Physical chemistry 138 

Physiological chemistry . . 146 

Polariscope 139 

Polyatomicity 96 

Pottery 6 

Priestley 36,37,56 



PAGE 

Proportions, law of defi- 
nite 42 

Proust 63,99 

Prout's hypothesis 81 

Radiations : 152 

Radical theory 121, 122 

Radioactive substances . . . 153 

Radioactivity 149 

Radioactivity and peri- 
odic system 156 

Radioactivity, contribu- 
tions from 86 

Radioactivity, induced . . . 152 

Radium 151 

Ramsay 86, 113, 114 

Raoult 142 

Rayleigh 113 

Rays, action of 155 

Remsen 94 

Remsen on relation of 

elements 87 

Replacement value 95, 96 

Richter 60 

Rontgen 150 

Rutherford, 89, 154, 156, 159, 161 

Salt 5 

Saltpeter 5 

Saturation capacity 96 

Scheele 39, 40, 41, 103, 119 

Scheerer 77 

Schmidt 148 

Schiitzenberger 79 

Science, evolution of 1 

Sefstrom Ill 

Silbermann 93 



168 



INDEX 



PAGE 

Silver 3 

Soaps 7 

Soddy 86, 157, 159 

Solutions, properties of , . . 141 

Specific heats, law of 72 

Spectroscope Ill, 139 

Stas 77 

Stereochemistry 133 

Stromeyer Ill 

Structure, theories as to . . 126 

Substitution theory 126 

Sulphur 7 

Sulphuric acid 22 

Symbols 109 

Tanning 6 

Telluric screw 84 

Thales 13 

Thenard 103 

Theories 12 

Theory, rise of 30 

Thermochemistry 93 

Thomsen 93 

Thomson 77 

Thomson, J.J 160, 161 

Tin 3,4 

Tinctures 27 

Toth 9 

Transmutation of ele- 
ments 20, 21 

Travers 114 

Triads 83 

Trichloracetic acid 127 

Turner 82 



PAGE 

Type theory 129 

Unitary theory 128 

Universe and matter 159 

Urea, synthesis of 118 

Valence. . . .94, 97, 131, 156, 157 

Valence, evolution of 94 

van Helmont 27 

van Slyke 149 

van't Hoff 134, 143 

Vapor densities 75 

Vauquelin 147 

Vinegar 5 

Vogel 79 

Volumes, law of 67, 68 

Waage 140 

Water, composition of ... . 48 
Water, transmutation of . . 49 

Wilhelmy 140 

Williamson 95, 96, 130, 141 

Wohler Ill, 118, 119, 127 

Wollaston 72 

Wood 11 

World building 16 

Wurtz 96 

Wurtz, study of amines . . 97 

X-rays 150, 153, 155 

X-ray spectra 87 

Zero group 86, 112, 113 

Zinc 3 

Zosimus ! 18 



H 187 83 







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